Add last_motion_event to the MotionEvent class.
Add last_touch
Implement last_touch in button behavior
Merge branch 'last_touch' of https://github.com/matham/kivy into matham-last_touch
behaviors: move back last_touch to ButtonBehavior. Ensure the last_touch is set _before_ the on_release/on_press event are dispatched. Remove the last_motion_event, its not helping the purpose of the PR.