windowManager: Add switch-to-application-n keybindings

Having Unity-like shortcuts for activating the first nine applications
in the dash has been a long requested feature, but somehow nobody got
around to implement it.

As the shortcut is most useful outside the overview where the dash is
not visible, only consider favorite apps as they have a predictable
order.

https://bugzilla.gnome.org/show_bug.cgi?id=648000
1 job for wip/fmuellner/fav-shortcuts in 1 minute and 36 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Source Check
passed #205983
js_check

00:01:36