Add mouse move event and implement screen picking.

This commit adds the 'pointer.move' event to the Input service, thanks
to Nate. This event passes the page X and Y coordinates to the handler
and may be used to fire rays into the scene for object picking as demonstrated
in the updated test scene.
Merge branch 'master' of https://github.com/dkushner/amoebadome

Conflicts:
	index.html
	js/input.js