Find a way to use WebglRenderer.

[stephank]

There's already a very simple working WebGL renderer implementation in src/client/renderer/webgl.coffee, but it's currently unused. It was built and tested exclusively on Chromium 6.

Performance was mostly identical to the current default renderer, for me at least. I wonder if it's faster for anyone, and if it can be a sane default in certain scenarios.

Once there's a lobby or some sort of settings GUI, there could be a switch to enable it there.