Add a cull step for shadow casters.

* Actually PSSM with a shadow distance of 400m, renders a 1km x 1km x 1km on last cascade of shadow map.
* This cull reduce lots of draw calls.
* TODO:
```
class SceneCullingState
{
   ...
   static PlaneSetF mExtraPlanesCull; // TODO MSVC 2012 memory corruption without static
   ...
};
```
Changes on Forest for use cull for shadow casters.
Merge branch 'cull_shadow_casters' of https://github.com/BeamNG/Torque3D into lightingExperimentation