Improve performance

[stevenhauser]

Game and especially editor performance are pretty bad with larger levels. Need to make sure we're handling immutability and component purity correctly. Tons of ideas on how to improve this. DOM itself could be the problem though due to massive number of nodes.

[stevenhauser]

A lot of the core problems were addressed in #10, but there's still a lot that can be done such as not rendering every single tile like a nincompoop, combining ground and entity DOM nodes, etc.