Improved normal smoothing

[Shfty]

Currently, smooth mesh normals are generated on a per-brush basis, meaning that artifacting occurs on contiguous shapes made up of multiple brushes (such as the arch in the test map).

This can be solved by combining these brushes into a single mesh, stripping away non-visible faces, and calculating smooth normals on a per-triangle basis.

Need to think on a solution, as this is non-trivial QBSP-esque functionality.

[Shfty]

Not feasible for now- Qodot works in brushes, so this is better left to something else like eventual BSP support.