Internal Changelog:
- A scene now has a maximum amount of render texture. It is to be
rendered in order of the array by the engine.
- A scene now needs an explicit render system to draw onto the render
textures. The scene will also init the number of render layers
needed.
- The change is to allow more separate of concerns when it comes to
rendering. A scene can also now compartmentalise the rendered items,
which hopefully make understanding the code easier.
- Update all exisiting code to use the new render system.
En Yi