Move data structure to Python

[jonmaddock]

The data structure needs to move from Fortran module variables to Python class attributes for the physics and engineering modules.

Once the physics/engineering modules have been converted to Python, their corresponding module variables will be in separate Fortran modules, e.g. tfcoil_variables.f90. These need to be incorporated into the new TFCoil Python class as attributes.

Due to the one-way nature of the Python-Fortran interface, it needs to be worked out how this can be done in incremental steps without completely unravelling the Fortran module variable dependencies and having to convert all variables in one go. Hopefully with some careful thought most modules can be converted one-by-one to minimise risk.

• Determine strategy
• Recreate Fortran-Python dicts without Fortran source parsing #3499