Optimise wavefield sampler depth calculations

[srmainwaring]

The depth calculation using the WavefieldSampler accounts for about 18% of the compute time in the hydrodynamics update. This issue is to track improvements to optimise performance.

• Axis align the water patch with the coordinates used for the link / collision mesh
• Create version of water patch and grid that does not require CGAL
  • Assume that the line search is always along one axis (z)
  • Take care with floating point comparisions when determining the cell / triangle each vertex projects into
  • Precalculate normals and plane equations for each triangle