Implement global gestures (for swiping in and out the shell's overview and quick-settings)

We want to have swipe gestures to pull in the overview from phosh's home bar and the settings menu from the top-bar which are likely best implemented in the compositor directly.

(filing this issue since there were discussions here and there but we don't have anything to track it yet)

Related https://source.puri.sm/snippets/95

hacky demo: https://social.librem.one/@agx/103974952717123533