media-keys: Add support for Killswitch media keys

Add support for the XF86Bluetooth, XF86WLAN and XF86UWB media keys.
The first one will toggle Bluetooth on/off, as the Bluetooth panel does,
the latter ones will toggle the global software killswitch.

The reasoning behind those 2 keys toggling the global software
killswitch is that:
- we don't have a killswitch for only WiFi
- there are very very few laptops with a UWB killswitch button, if
  anyone actually remembers what UWB actually is
- there are no XF86 keys for the global killswitch, so they usually get
  mislabeled as the WLAN killswitch

https://bugzilla.gnome.org/show_bug.cgi?id=661643