Added infrastructure for passing current density to shaders, Fixed brigh...

...t dense atmospheres, fixed hard surface normals based on density


This will fix #1906 + reinstated the surface normals based on density.

Good way to test this is doing a decent into Venus, Titan or Atlantica.

@Luomu I didn't manage to tie this to Camera, so I used player, can you take a look and maybe adjust so it will work the way you wanted it?