Add object reference in evt_handler func call

[hi-liang]

Currently args passed are scene, evt, msg.

While it's possible to query the scene objects dict for evt.object_id it seems like it would be easy to just pass the reference directly since that lookup is already performed, maybe just tack on obj as attribute object to the event

arena-py/arena/scene.py

Lines 141 to 142 in 743eaee

	if obj.evt_handler:
	self.callback_wrapper(obj.evt_handler, event, payload)