Make akonadi_control a qguiapplication for session management
Review Request #125746 - Created Oct. 21, 2015 and submitted
As suggested on the mailing list, make akonadi_control a QGuiApplication to make it exit with session.
AkGuiApplication is not used here, because AkApplicationImpl<QApplication> which will pull in unnecessary Qt5::Widgets dependency.
Also disable session auto restart since akonadi_control is started on demand.
No more remaining akonadi process after logout.