Better JSON parsing, simpler new type support

This MR provides much better property parsing.

• Use proper python - json - C++ types when parsing, with nlohmann::json functionality.
• nlohmann::json natively supports a richer variety of types than the previous custom-made translations: https://json.nlohmann.me/features/types/
• Supporting new types in JSON can be done by adding a to_json and from_json in case the types are not known to nlohmann::json. This MR only introduces one such conversion for type BankTypes.
• Generated json files with --write-config are now reusable as input files.
• Properties should now be supplied with their proper type in python configurations as opposed to "always string".

Closes #179 (closed)

Required for #305 (closed)