switchGestures: Do not hard-code allowed modes

switchGestures: Do not hard-code allowed modes

The touch/touchpad gestures to switch workspace currently hard-code
the modes in which we want the gestures to work. While these modes
are correct, the existing switch animation only works in NORMAL mode,
not in the overview where the window group is hidden. The easiest way
to address this is to handle both cases completely separately, namely
use separate actions in- and outside the overview.

Make the existing usable in that way by making the list of allowed
modes a constructor parameter.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/516