[FEATURE] implement curved / segmented faults from depth observations in LoopStructural

[GeoMattB]

Faults generated using interpreted depth data points, either from seismic interpretations or 2D potential fields forward / inversion modelling aren't currently supported well within Loop, particularly curved / segmented faults.

Implementing the tangent method put together by Lachlan within LoopStructural so Loop is aware of the segmented faults. An example of the method outside of LoopStructural is here:
https://github.com/GeoMattB/Loop_fault_test

Lachlan, this is just what we've discussed, dropping it here so we can track it. Thanks for your help.