Add geometry simplification

[jamiebull1]

Too much detail in geometry leads to slow simulations. It would be great to have a way of simplifying geometry while maintaining topology (adjacencies).

The shapely library, which is already a dependency for geomeppy, has some functions which may be useful.

simplify() - https://shapely.readthedocs.io/en/latest/manual.html#object.simplify
snap() - https://shapely.readthedocs.io/en/latest/manual.html#snapping