Turn PUF into pickle loader, drop global var definitions

[iliakur]

I think it makes sense to read in the variables we define in PUF from some sort of file. We currently have JSON and pickle at our disposal, so it's not like we're short on options.
This will make the code more readable (less scrolling through tedious variable definitions) and we can always choose a file format that's human-readable so that interested parties can inspect what variables we are loading.

Additionally, just like in issue #10 it would be nice to get rid of global variable definitions and replace them with a dictionary. It would make sense to merge this dictionary with the one we get from the PUF file.

[iliakur]

Closing this, as we have the code for it but also may find another solution.