Blender Git Loki

Fixes for using tablet events in keymap

* Need to classify tablet events as being in the "mouse" category, or else attempts
to add a new keymap item for this will fail by reverting to keyboard input

* Made event matching more restrictive - it will now trigger only on a tablet events
for LEFTMOUSE events. The problem was that, even when hovering over the tablet
and pressing a key, you'd still get an event with tablet data, which meant that
that event would get wrongly caught and handled.