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>
CardView: introduce a SlidingItemArea component to represent items that can be swiped out of the view. The main examples are the cards (swiped up), and the notifications (swiped left or right). The latter still have to be implemented.

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