Allow passing simulation settings via config files

[fhagemann]

In PR #594, we are introducing a way to pass the surface_refinement_limits used for the surface refinement via the config file, by storing it to sim.world. We might want to think about allowing for the same thing for all (?) keyword arguments of calculate_electric_potential! etc. such that the setting can also be saved to a file.
We might also think about storing the simulation settings used to the sim.config_dict (see also #435).