If you did not know the Wacom Express Key Remote (or EKR for short),
let me introduce it to you:
https://estore.wacom.com/media/catalog/product/cache/fb4143a007ae6439deba9b18afd745f2/a/c/ack-411050_main_2.jpg
This is a hand-sized standalone pad device, meant to be used together
with drawing tablets, providing additional buttons and a touch sensitive
ring that can be mapped to actions and keypresses.
These pads were so far handled in GNOME, but in a very subtle manner.
As the EKR is implicitly paired to a tablet, it was possible to map
EKR buttons from the paired tablet once the pad OSD UI from GNOME
Shell was shown.
As this device basically just needs a "Map buttons" action to
configure it, it just didn't sit well in the older Settings UI,
it would get a separate page with just a lone button in there. So
its support has been kind of an easter egg so far.
But the new UI can indeed accomodate better a device that is neither
tablet nor stylus, and has few options. This commit adds the EKR
as a separate AdwPreferencesGroup.
