Seperate "world" and "window"

[traverseda]

Right now the world is responsible for part of the rendering. It shouldn't be. We want it to be as simple as possible to implement new worlds.

[mrpudn]

Definitely - I tried to move the opengl stuff into Window with my last pull request, but I noticed some odd things when I did that.

I had trouble untangling a lot of stuff when I split up main.py, but I'd love for someone else to take a look at it :)