Prefabs and/or project level clone blanks

[davesmith00000]

At the moment, you need to register clone blanks on every frame you want to use them, which is inefficient if you plan to reuse the same things for the duration of the game.

We could allow clone blanks to be registered in the same way as, say, fonts, which would be more efficient.

I'm not sure what the delta is, but this might take us towards the idea of prefabs, and prefabs being the default way to render things because you get batching for cheap/free. Performance by default, essentially.