Implement the pointer-gestures-unstable-v1 protocol
This protocol relays touchpad gesture events produced by libinput to supporting clients (e.g. Evince, Eye of GNOME).
Tested with gtk3-demo and the apps mentioned above. I should probably reduce the duplication in the code, but by how much? swipe(…, BEGIN|UPDATE|END)
+ pinch(…, BEGIN|UPDATE|END)
or gesture(…, SWIPE_BEGIN|SWIPE_UPDATE|SWIPE_END|PINCH_BEGIN|PINCH_UPDATE|PINCH_END)
?