Add new touchpad gestures

[bala7s]

Currently only 4 finger left/right has a function, to swap between workspaces. 4 finger up could open the workspaces view and 4 finger down could close it. In macOS I really love touchpad gestures making me use the touchpad even when I use separate mouse too. I would like to see this in Cosmic too.

[git-f0x]

It's planned, but isn't yet implemented. The other 2 4-finger directions will be used for the workspaces overview and the App Library, and there'll also be 3-finger gestures (to switch app focus).