refactor and document: C4FoWLightSection only calculates the triangles now, C4FoWLight stitches everything together and renders

* intermediate fade triangles are now calculated in C4FoWLight
* rendering takes also place in C4FoWLight, using different C4FoWDrawStrategies
* solved an old TODO from Peter (int -> int32_t)
* refactor and simplify portions of the light vertex calculation code