Sprites and a loading screen and reset behaviour

Wow. All the things.

Now we have a loading scene that preloads sprites from spritemap : maps
coords in the sprite map (based on w/h) to names. These seem to be
treated as regular components and assigned to the relevant entity in the
game (like tree etc).

Also now have game reset behaviour. So when you hit a key you can
restart. This has to unbind previously bound events which is a bit icky
but good to know that's a problem.