Caustics adjustments in LightMix

The idea is to have caustics-specific controls in LightMix. Either:

• Caustics color and intensity adjustments for each LightSelect element. This way, caustics color and intensity could be changed for each light, independently from that light's color and intensity.
  
  or

• A global caustics adjustment which can change the intensity and color of all caustics visible in the rendering.

This could work when the caustics solver is enabled and you generate LightMix.

It would be “better” than the Render Setup > Performance caustics multipliers because it would make it possible to adjust caustics during and after rendering, without the need to re-render.