[Py] Manage parameters like matplotlib #1651

Is your feature request related to a problem? Please describe.

The current mechanism to set parameters is a bit confuse and verbose. When setting up a simulation, parameters are intertwined with instructions to set up initial conditions, which is not ideal for clarity.

Describe the solution you'd like

A mechanism similar to matplotlib's rcParams would allow to set up clean parameter files while leaving the possibility to change the parameters in the python script for flexibility.