Provide a KCM for Drawing Tablets

Otherwise called Wacom tablets, that is. This is using the same InputDevice dbus interfaces we use for the mouse and touchpad kcms.

This is an initial approach to it, and some other features could still be added. Nevertheless these work as is so we can merge, test and iterate. (Others are button re-mapping, calibrating and setting the area).

Depends on KWin's kwin!1604 (merged)

Pinging the artists that were around on the meeting last week. @hanyoung @davidrevoy @tysontan @woltherav

Addresses topics on https://phabricator.kde.org/T14971