Graphics system debugging

[bhousel]

We have an issue already in the Rapid repo for showing better stats to help us understand the graphics system, but I could see this being a great use for a new tab in the dev tool.

It would be great to know how many features we're drawing, what kind they are, textures in use, how much time we're spending in different parts of the code, how efficient pixi is batching the draw calls, what is the effective frame rate, and maybe a general "stress on the system" metric that we can use to adjust what gets drawn or culled.

facebook/Rapid#450