mail_daemon: IMAP delete messages on the server only when delete_remote_when_local setting is set

Change-Id: I88fcc7a185cede080af7c3b85f9466a02f895809
Reviewed-on: https://review.haiku-os.org/674
Reviewed-by: Stephan Aßmus <superstippi@gmx.de>

IMAP: make the body fetch limit setting available.

* This is set by the ProtocolConfigView -- there should really be
some constant for this.

IMAP: Use useful default without destination.

* We now use the account name as destination directory.
* Turns out that an empty string is written as destination which worked
around the GetString() solution.

imap: added Settings::MaxConnections()/IdleMode().

* Also made use of the new BMessage API for the existing methods.

IMAP: Early work in progress of main protocol class.

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: make the body fetch limit setting available.

* This is set by the ProtocolConfigView -- there should really be
some constant for this.

IMAP: Use useful default without destination.

* We now use the account name as destination directory.
* Turns out that an empty string is written as destination which worked
around the GetString() solution.

imap: added Settings::MaxConnections()/IdleMode().

* Also made use of the new BMessage API for the existing methods.

IMAP: Early work in progress of main protocol class.

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.