IMAP: Remove direct usage of OpenSSL.

It already uses BSecureSocket without checking for USE_SSL,
so just assume we have SSL no matter what.

IMAP: fixed folder configuration.

* Store the settings, don't archive the view; removed leftovers of the
old settings API.

Improved label of the button to configure the IMAP folders.

Adapted IMAP to the new MailSettingsView API.

Work in progress of mail rework.

* Not everything compiles; all protocols, and inbound filters do, though.
* Renamed a few classes to give a better idea what they are for; prefixed
public classes with the 'B' prefix.
* Moved ProtocolConfigView's classes into the BPrivate namespace.
* Moved BMailFilter into its own file.
* Added BMailFilter::DescriptiveName(). This is now used by the RuleFilter
in order to give a description of what it's doing (ie. no more dozens of
"Rule filter" entries in the preferences).
* Removed no longer used MailAddon.h.
* Renamed Addon to AddOn where found, since that is more consistent with the
rest of the API.
* Merged the former MailProtocol with the former MailProtocolThread; the
differentiation between those two was pretty messy.
* All configuration views touched so far are now using the layout kit.
* The RuleFilter is currently broken functionality wise; I have not yet decided
how to solve the stuff it uses (TriggerFileMove() does not exist anymore,
for example).
* BMailAddOnSettings (formerly known as AddonSettings) now directly subclass
BMessage; there are no Settings() and EditSettings() method anymore. The
class uses a copy of itself to determine whether or not it has been changed.
* Lots of cleanup.

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.

IMAP: fixed folder configuration.

* Store the settings, don't archive the view; removed leftovers of the
old settings API.

Improved label of the button to configure the IMAP folders.

Adapted IMAP to the new MailSettingsView API.

Work in progress of mail rework.

* Not everything compiles; all protocols, and inbound filters do, though.
* Renamed a few classes to give a better idea what they are for; prefixed
public classes with the 'B' prefix.
* Moved ProtocolConfigView's classes into the BPrivate namespace.
* Moved BMailFilter into its own file.
* Added BMailFilter::DescriptiveName(). This is now used by the RuleFilter
in order to give a description of what it's doing (ie. no more dozens of
"Rule filter" entries in the preferences).
* Removed no longer used MailAddon.h.
* Renamed Addon to AddOn where found, since that is more consistent with the
rest of the API.
* Merged the former MailProtocol with the former MailProtocolThread; the
differentiation between those two was pretty messy.
* All configuration views touched so far are now using the layout kit.
* The RuleFilter is currently broken functionality wise; I have not yet decided
how to solve the stuff it uses (TriggerFileMove() does not exist anymore,
for example).
* BMailAddOnSettings (formerly known as AddonSettings) now directly subclass
BMessage; there are no Settings() and EditSettings() method anymore. The
class uses a copy of itself to determine whether or not it has been changed.
* Lots of cleanup.

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.