Initial optimisation of FFT wave model and correct normal orientation

This PR has an initial round of optimisation of the FFT wave model and corrects the orientation of the vertex normals.

Details

A number of redundant loops are removed
The tangent space is calculated using the derivatives computed using FFT rather than finite difference
The orientation of the normal vector is corrected (reversed in sign)
Remove shadow casting from the world axes
Add a test environment map for checking surface normals and tangent vectors
Keep original unoptimised version as reference implementation
Add tests that cross check optimised functions against the reference versions