Load model from .json file

[flohorovicic]

Is your feature request related to a problem? Please describe.
Add functionality to load (or create) model from .json file. Should ideally be complemented with a corresponding "save model to .json file"

Describe the solution you'd like
A method to create a model object with complete functionality (up to gp.compute_model(model)-step) from a .json file. Important to save/load models, and as a more flexible input/ output feature (instead of multiple .csv files, corresponding python-scripts, etc.).

Describe alternatives you've considered
Current state, which requires too many different files and is, therefore, error-prone.

Additional context
XML formats would also be possible, but I believe .json is a good choice between flexibility and strictness (with enforced schemas).

[flohorovicic]

See ongoing developments in https://github.com/flohorovicic/gempy/tree/feature/json_io

[flohorovicic]

Current state: possible to load data (surface and orientation), model metadata, layer stack and regular grid from .json. Tests not complete, yet.

[flohorovicic]

Full functionality for simple model (single structural group) completely implemented, including complete set of default values.