Proposal: Material render layer overwrite.

[mintlu8]

Let a material optionally set its own RenderLayer, as opposed to the RenderLayer component that applies to all materials on a mesh.

Why

This is a simple way to add a custom prepass. For example if I want to draw outline around a mesh that I'm hovering, I can add a material that draws white on a separate layer, then I can use that texture in another shader or during postprocessing for edge detection.