WIP: Reducing GC in TrackRenderer.
WIP: sensible names, plus only one TrackRenderer.
WIP: removed the need for FloatArray for vertices.
WIP: Removed "obscuring" code.

I am not convinced if the code to detect whether a car is obscured is worth it,
particularly given that drawing the car's alpha version each time is almost indistinguishable
 from doing the calculations.
WIP: The CarRenderer is only created once per WorldRenderer.
WIP: WorldRenderer only created once per Playing state.
WIP: World only created once per Playing.
Merge branch 'feature/gc_reduction' into develop