Added MOUSEPAN (the trackpad event) to control propertional size while transform.

There's many hardcoded scrollwheel events in Blender for this, and with new proper
analog trackpad handling I'll try to find good remapping for most cases.



git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53483 954f8c5b-7b00-dc11-b283-0030488c597c