Add some accessors to simplify common tasks for GestureAction users:
• clutter_gesture_action_get_motion_delta() to get the delta
on the X and Y axis in stage coordinates since the last motion
event, and the scalar distance travelled;
• clutter_gesture_action_get_velocity() to get an estimate of the
speed of the last motion event along the X and Y axis and as a
scalar value in pixels per millisecond.
https://bugzilla.gnome.org/show_bug.cgi?id=681648
GestureAction supports a single device/touch point. We'll need touch
events supported in Clutter before adding the ability to set required
device/touch points on gestures.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2585
The GestureAction is marked as abstract, but it has a constructor. It
should be possible to create simple gesture recognizers through signal
handling alone, so we might as well have GestureAction be a concrete
class from the start.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2585
