Future: CameraSystem + changed support

[ikeycode]

We should implement a 'changed' modifier so that we can skip iteration of unchanged chunks.
This will allow us to do some hackery whereby we update transformed positions of components on-demand in a system only when they've been changed, and use this cached data in the renderers.

[ikeycode]

FWIW this isn't a bottleneck right now but it'll come in handy for .. other.. stuff.