More work on the folder views:

- Splitted the FolderView context menu filling operations in few virtual functions. Some of them are now overridden by child classes.
- Grouped the menu items logically and reordered them a bit.

IMO the menu is more readable now (need comments on this tough).
- FavoriteFoldersView can rename and remove entries again.
- Renamed and moved qobject_reconnect the Util namespace since it's used in multiple source files now.
- Some cleanups and documentation.