Summary:
This change adds global touchpad swipe gestures to the
GlobalShortcutsManager and hooks up the swipe gestures as defined at the
Plasma Affenfels sprint:
 * swipe up: Desktop Grid
 * swipe down: Present Windows
 * swipe left: previous virtual desktop
 * swipe right: next virtual desktop

The main work is handled by two new classes: SwipeGesture and
GestureRecognizer. This is implemented in a way that it can be extended
to also recognize touch screen gestures and pinch gestures.

The SwipeGesture defines what is required for the gesture to trigger.
Currently this includes the minimum and maximum number of fingers
participating in the gesture and the direction. The gesture gets
registered in the GestureRecognizer.

The events for the gesture are fed into the GestureRecognizer. It
evaluates which gestures could trigger and tracks them for every update
of the gesture. In the process of the gesture tracking the
GestureRecognizer emits signals on the Gestur...