fix airbrush + tablet pressure bug.

Timer events used by the airbrush would always give a pressure of 1.0, ignoring the tablets real pressure in all paint modes.

Move tablet data into its own struct-member so it can be used with timer events.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53870 954f8c5b-7b00-dc11-b283-0030488c597c