Gesture Improvements

This is a meta issue to track improvements to the gesture system. (Because I'm waiting on reviews and starting to lose track of when I can work on what. I think having it public also won't hurt so feedback or more linked issues is welcome :))

- [x] #2074

Docks related:
- [x] #2239 which then allows for
- [x] #1003
- [ ] #225

Better Touchscreen gestures:
- [ ] #2629
- [ ] #1959
- [ ] #1272
- [ ] #1801

Misc:
- [x] Interruptable animations #1202
- [x] MultitaskingView workspace switch: #2161
- [x] Multitasking view open/close
- [x] Desktop workspace switch
- [x] Touchpad gesture backend in gala (drop touchegg)
- [x] #2164

Bug Fixes:
- [x] #2149
- [x] #2148
- [x] https://github.com/elementary/gala/issues/544

Regressions:
- [x] https://github.com/elementary/gala/issues/2399