Reduce repetition of shared methods in well.py

@connortann - the changes to surface.py involve a lot of repetition, with exactly the same method appearing in TriangulatedSet, Mesh and PointSet. Keen to hear any suggestions for how to improve this (the best I could think of was adding a Parent class for these three classes to inherit from containing the shared method). Similarly the methods in well.py for BlockedWellbore, WellboreFrame and Trajectory are very similar, so it may be possible to improve these too

_Originally posted by @emmanesbit in https://github.com/bp/resqpy/issues/50#issuecomment-856047182_