This commit adds the following features:
* Folder creation,
* Folder modification,
* Folder removal.
There are still issues with subfolders but they should not be too complicated to fix.
I've also done some javascript refactoring.
* Dragging multiple messages is now possible
* Better email displaying (headers and body are now displayed at the same time...)
* Bugfixes about dropdown menus
* Misc. enhancements.
Antoine Nguyen