phone vs 'docked' mode

In order to implement things like https://gitlab.gnome.org/Teams/Design/os-mockups/-/commit/fe9c4089a099827748d7bb7a8bdc763f4771c69d we should have a switch that puts us in either mode. This can also be used for toggling swipe gestures vs. on top and bottom bar. This will mostly infuence top and bottom bar.