window management rework

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Gestures for the GestureArea component

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
QML: rename Compositor as WindowManager, and take C++ compositor as input property of root object

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