Global parameters file

[ray-chew]

Information on common parameters is currently duplicated across input files.

This issue moves common parameters to a common location, with attention to:

• Physical Constants
• Required parameters
• List of valid choices (e.g. bcs, ...)

[ray-chew]

I decided not to go with python-decouple or an external config file because UserData and sol_init must be Python objects, so the user can be expected to also change the simulation settings in a Python environment.