first shot at fullscreen + pointer lock

a button activates fullscren & pointerlock

this is still pretty messy with vendor-prefixes and two different
ways the canvas is scaled when going fullscreen. so i needed a div wrapper
to make them look the same (both as default in chrome... somewhat)

there's lots of debug code

if fullscreen is enabled, the mouse becomes invisible and movementX
movementY are set on mousemotion events