Improved folder config window a bit.

* Now uses the BLayoutBuilder instead of ALM layout - not only is the code much
simpler now, resizing the window isn't as sluggish anymore (less flickering).
* Fixed a drawing bug in the list view; the drawing state wasn't properly
maintained, leading to rendering artefacts.
* Moved the checkbox to the start of the line.
* Use B_ASYNCHRONOUS_CONTROLS for all windows.
* Fixed a few typos.

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.

Improved folder config window a bit.

* Now uses the BLayoutBuilder instead of ALM layout - not only is the code much
simpler now, resizing the window isn't as sluggish anymore (less flickering).
* Fixed a drawing bug in the list view; the drawing state wasn't properly
maintained, leading to rendering artefacts.
* Moved the checkbox to the start of the line.
* Use B_ASYNCHRONOUS_CONTROLS for all windows.
* Fixed a few typos.

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.