Vertex normals are being incorrectly generated for vertical faces

[DummkopfOfHachtenduden]

This might be an issue with normals / backfaces or geometry itself.

• Some objects like the grass is not lit at all.
  

• Trees are partially lit.
  https://www.youtube.com/watch?v=LtbeeqO5Ywc

[hogsy]

Looks like a fault with the normals generation.

[hogsy]

Partially depends on #124 as there are some cases which our automatic normals generation can't deal with unless we handle specific cases (e.g. generate face normals for boxes etc.)

[hogsy]

Amendments have been made which will alleviate this issue in some cases. Closing in favour of #124