Optimize shaders

[Voxar]

We use a single shader hacked up by @Voxar who really doesn't know a lot about shaders. It is likely super inefficient due to a lot of extras and experimentations and used as an all-in-one.

I'm thinking it should probably be split into a number of smaller shaders optimised for some often used simple materials that doesn't need the full PBR calculations, low performance ones for quest1 and equivalent headsets, and so on.