Participating media II

I managed to get participating media properly, well at least how I expect it to work.

Since there are only two weeks left before I have to hand in the final report I will probably stop implementing anything new and continue working on the report.

I will however try to create cover art to demonstrate the features that I have implemented thus far.

Voxel grid rendered using henyey-greenstein phase function g=-0.4
Constant volume; the light is coming from the top-right
Test render for proper occlusion with surfaces