VRayMtl : Self-illumination

[Morne]

@Macker

IMHO would be smarter to implement in form of a map. It would keep VrayMTL UI uncluttered, and at the same time, the map could serve more purposes, such as doing the same for backplate in environment slot.

Not sure what you mean. It already has a map you can plug into it, a GI tick, and a multiplier. The multiplier is the problematic one here as it requires guessing and/or test renders