IMAP: Use BStringList instead of STL vector.

IMAP: let mail retrieval scale better.

* We now also maintain a mail index -> UID array in IMAPMailbox.
* Instead of fetching the message entries by a fixed range of UIDs, we use the
message count, and get the entries by index.
* Likewise, in FetchHeadersCommand, we now get a list of UIDs rather than a
range. This makes it possible to only download exactly the headers we want.
* Extended FetchCommand to be able to dynamically build a sequence list from
a list of UIDs.
* Besides the suboptimal body fetching (one at a time, due to holes in the
IMAP specification), we should now be able to retrieve the messages with
pretty much optimal performance, while retaining an acceptable responsiveness
to user requests.

IMAP: FetchMessageEntriesCommand now also works without UIDs

* This will be used to solve the TODO in CheckMailboxesCommand::Process()
when the initial message sizes/flags are retrieved.
* Also fixed imap_tester build.

IMAP: work in progress of downloading the mail body.

* Most things are in place now, we just try to download the body to the
wrong file, as the final location is currently unknown.
* Added local only kPartialMessage flag for mails, but it's not being
used yet.

imap: Fetching headers is now working.

* No state is stored yet, though, so that all messages will be downloaded
over and over again.

imap: WIP of getting fetching headers to work.

* Changed the FetchListener mechanism quite a bit.
* Doesn't seem to work correctly yet, although most pieces are in
place now.

imap: Testing for new messages is now working.

* There is now a CheckSubscribedFoldersCommand that is issued on the main
connection that triggers everything.
* The new CheckMailboxesCommand divides the new mail check into several
portions, and requeues itself until the next step, ie. the
FetchHeadersCommand.
* The headers of the new mails are downloaded, but nothing is done with
them yet.
* The actual check for the new mails doesn't scale that well yet, not sure
how to properly do this without having to rely on the mail indices. Might
be sensible to solve this via some simple heuristic.

imap: Fleshed out command processing.

* Still doesn't do anything useful, though.

imap: Work in progress of connection setup.

* SelectCommand now correctly encodes the mailbox name again.
* Hierarchy separators from the LIST/LSUB commands are now properly parsed,
and taken into account.
* Folders in the file system are now created for mailboxes on the server,
supporting hierarchical mailbox names.
* A connection worker now has an IMAPFolder that handles the local side of the
mailbox, and an IMAPMailbox that handles the server side.
* Connection workers are now created/deleted, and setup correctly. They will
now also wait in case they don't have a mailbox until they get some.

Use GETQUOTAROOT instead of GETQUOTA.

* At least with my ISP, there is no "" root, so the command would fail when used
as is.
* Now we always use the GETQUOTAROOT command instead, by default for the INBOX
mailbox. This isn't entirely correct either, but better than nothing.

Added support for decoding RFC-3501 mailbox names.

* Added new RFC3501Encoding class that implements modified UTF-7 as specified
in RFC-3501; only decoding is implemented right now.
* ListCommand now uses this new class to encode, and decode the folder names.

Started working on the IMAP add-on itself.

* Renamed imap_config.cpp to ConfigView.cpp, IMAPFolderConfig.(h|cpp)
to FolderConfigWindow.(h|cpp).
* Got the latter to build.
* Added Settings class to simplify and unify the BMessage based
settings access.
* Removed the InboundProtocol[Thread] implementation from the build for now.

Read some more specs, cleaned Protocol a bit.

* Added some TODO comments based on the various IMAP specs and extensions.
* Removed SelectMailbox() functionality from the Protocol class; it's not
really useful to have it there.
* Removed some other methods that don't belong into the Protocol class.

More work in progress of the IMAP rework.

* Implemented FetchCommand, and some more.
* Improved and extended the imap_tester.
* The base to implement the new InboundProtocol on is now mostly done, at least
for a start.

Got rid of the ConnectionReader, and implemented parsing literals.

* The parser now works on a BDataIO instead. It's now even a bit simpler
overall.
* Implemented ParseLiteral() - the default implementation just reads the data
into a string. Thanks to BDataIO this was now very simple to do.
* Tested the code: imap_tester can now successfully read mails (using the raw
command only, at the moment).

Work in progress of rewrite; IMAP doesn't even compile at this point.

IMAP: let mail retrieval scale better.

* We now also maintain a mail index -> UID array in IMAPMailbox.
* Instead of fetching the message entries by a fixed range of UIDs, we use the
message count, and get the entries by index.
* Likewise, in FetchHeadersCommand, we now get a list of UIDs rather than a
range. This makes it possible to only download exactly the headers we want.
* Extended FetchCommand to be able to dynamically build a sequence list from
a list of UIDs.
* Besides the suboptimal body fetching (one at a time, due to holes in the
IMAP specification), we should now be able to retrieve the messages with
pretty much optimal performance, while retaining an acceptable responsiveness
to user requests.

IMAP: FetchMessageEntriesCommand now also works without UIDs

* This will be used to solve the TODO in CheckMailboxesCommand::Process()
when the initial message sizes/flags are retrieved.
* Also fixed imap_tester build.

IMAP: work in progress of downloading the mail body.

* Most things are in place now, we just try to download the body to the
wrong file, as the final location is currently unknown.
* Added local only kPartialMessage flag for mails, but it's not being
used yet.

imap: Fetching headers is now working.

* No state is stored yet, though, so that all messages will be downloaded
over and over again.

imap: WIP of getting fetching headers to work.

* Changed the FetchListener mechanism quite a bit.
* Doesn't seem to work correctly yet, although most pieces are in
place now.

imap: Testing for new messages is now working.

* There is now a CheckSubscribedFoldersCommand that is issued on the main
connection that triggers everything.
* The new CheckMailboxesCommand divides the new mail check into several
portions, and requeues itself until the next step, ie. the
FetchHeadersCommand.
* The headers of the new mails are downloaded, but nothing is done with
them yet.
* The actual check for the new mails doesn't scale that well yet, not sure
how to properly do this without having to rely on the mail indices. Might
be sensible to solve this via some simple heuristic.

imap: Fleshed out command processing.

* Still doesn't do anything useful, though.

imap: Work in progress of connection setup.

* SelectCommand now correctly encodes the mailbox name again.
* Hierarchy separators from the LIST/LSUB commands are now properly parsed,
and taken into account.
* Folders in the file system are now created for mailboxes on the server,
supporting hierarchical mailbox names.
* A connection worker now has an IMAPFolder that handles the local side of the
mailbox, and an IMAPMailbox that handles the server side.
* Connection workers are now created/deleted, and setup correctly. They will
now also wait in case they don't have a mailbox until they get some.

Use GETQUOTAROOT instead of GETQUOTA.

* At least with my ISP, there is no "" root, so the command would fail when used
as is.
* Now we always use the GETQUOTAROOT command instead, by default for the INBOX
mailbox. This isn't entirely correct either, but better than nothing.

Added support for decoding RFC-3501 mailbox names.

* Added new RFC3501Encoding class that implements modified UTF-7 as specified
in RFC-3501; only decoding is implemented right now.
* ListCommand now uses this new class to encode, and decode the folder names.

Started working on the IMAP add-on itself.

* Renamed imap_config.cpp to ConfigView.cpp, IMAPFolderConfig.(h|cpp)
to FolderConfigWindow.(h|cpp).
* Got the latter to build.
* Added Settings class to simplify and unify the BMessage based
settings access.
* Removed the InboundProtocol[Thread] implementation from the build for now.

Read some more specs, cleaned Protocol a bit.

* Added some TODO comments based on the various IMAP specs and extensions.
* Removed SelectMailbox() functionality from the Protocol class; it's not
really useful to have it there.
* Removed some other methods that don't belong into the Protocol class.

More work in progress of the IMAP rework.

* Implemented FetchCommand, and some more.
* Improved and extended the imap_tester.
* The base to implement the new InboundProtocol on is now mostly done, at least
for a start.

Got rid of the ConnectionReader, and implemented parsing literals.

* The parser now works on a BDataIO instead. It's now even a bit simpler
overall.
* Implemented ParseLiteral() - the default implementation just reads the data
into a string. Thanks to BDataIO this was now very simple to do.
* Tested the code: imap_tester can now successfully read mails (using the raw
command only, at the moment).

Work in progress of rewrite; IMAP doesn't even compile at this point.