Make SATNUM regions in FlowNet based on region parameter from simulation model

[olelod]

When setting the scheme to regions_from_sim the SATNUM regions in the input simulation model were used to generate the SATNUM regions for the FlowNet model. This PR makes this more flexible by allowing any region parameter from the INIT file to be used.

Contributor checklist

• [x] :tada: This PR closes #392.
• [x] :scroll: I have broken down my PR into the following tasks:
  • [x] Add region_parameter_from_sim_model to config_parser.py
  • [x] Add checks to config_parser.py
  • [x] Change the generation of SATNUM regions for FLOWNET to use the region_parameter_from_sim_model instead of the previously hard coded SATNUM
• [ ] :robot: I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR.
• [x] :book: I have considered adding a new entry in CHANGELOG.md.
• [ ] :books: I have considered updating the documentation.

[olelod]

Currently the implementation is such that you define a single prior which is used for all regions. I have not implemented a possibility for different priors in different regions (such as the one for equilibrium regions). I am open for doing that, but maybe make it an issue for further work?

[wouterjdb]

Currently the implementation is such that you define a single prior which is used for all regions. I have not implemented a possibility for different priors in different regions (such as the one for equilibrium regions). I am open for doing that, but maybe make it an issue for further work?

That sounds like a good idea. Just make it an issue, and leave it on the backlog for the time-being.