Introduce states for WindowManager, rename NotificationArea to Dashboard

 * states are now used in WindowManager, for a better description logic: "dashboard", "cardview", "fulllauncher","maximized", "fullscreen"
 * the LunaGestureArea qml has been moved near WindowManager, and the LunaGestureArea shouldn't now be used directly outside the WindowManager
 * NotificationArea has been renamed to Dashboard, as it better fits the description


Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>