altTab: Take over cycle-windows/cycle-group keybindings

The code to handle cycling through windows without showing a popup
was removed from mutter a while ago, which left the corresponding
keybindings mostly broken (i.e. they now only switch between two
windows). With the various switch-foo keybindings handled by the
shell, it is now easier to take over the cycle-foo keybindings as
well.

https://bugzilla.gnome.org/show_bug.cgi?id=730739