Added support for pinch in/out gestures

[oryasida]

Initial support for pinch in/out gestures. libinput does differentiate between 2/3/4 fingers pinch events so adding support for all the different variations can be done, but reliably executing the different variants isn't really easy.

[Coffee2CodeNL]

I was actually holding off on this one because pinch events aren't reliably picked up by libinput yet and I wanted to look if I could implement pinch/rotate events on my own via raw input, for this I'm communicating with the libinput maintainers

[oryasida]

I did notice that pinch events are a little iffy sometimes. Also played around with the rotate events pinch gestures, and noticed that the libinput_event_gesture_get_angle_delta function would sometimes return a high value if you just place to fingers and wiggle them a little (without really changing the angle between them), so doing something like volume control (when you don't wait for the fingers to lift of the pad - before receiving the end event) doesn't work nicely.