If a sequence moves past a certain distance without being used by a
gesture, reject it so clients may see and react to it ASAP. This makes
gestures to be began by initially quasi-static touchpoints, in addition to
quasi-simultaneous.
This object tracks both touch sequences happening on the stage and
gestures attached to the stage actor. When a gesture emits
::gesture-begin, All triggering sequences and future ones will be
marked as "accepted" by the compositor, and events will be listened
for meanwhile there are active gestures.
If a sequence goes unclaimed for a short time, it will be
automatically "denied", and punted to the client or shell element
below.
