HAT/MHW globally

[matth-love]

Currently, there is no support for global HAT/MHW transformations.

• Using the data from https://www.seanoe.org/data/01005/111620/; we should be able to grid this with RBF.

[matth-love]

Have added a 'fallback' just to get estimates, using HAT-symmetry-estimation. This is NOT CORRECT, but is pretty close, so using that for now until we can get a better solution.