Geometry system

[bcych]

Create a new module called geometry.py. Here's how it could work:

geometry.py

• New class called Ellipsoid, takes PRO and OBL as arguments. Could inherit from some base class called Geometry.
• Other polyhedra could be added to this module.

energy.py

• Ed() could be made a method of Ellipsoid
• demag_factors could be made a method of Ellipsoid
• get_material_parms() should be changed to take a geometry

Many other functions would need to be adjusted to remove PRO, OBL from the arguments and instead take a geometry.

Note that some fiddly stuff will have to be done with jax as I think you can't decorate a method - may have to call an additional function.