ENH: Initial integration of IHCantrabria wave functionality

- Wave models significantly restructured and refactored into a hierarchy of run-time selecatable models
- Gravity no longer hard-coded
- Ability to use any direction as the gravity direction
- Boundary conditions simplified and take reference to the wave model
  - removes a lot of code duplication and new code is ~30% faster
- Removed unused functions

Requires further testing
- Restart behaviour needs to be addressed