Allow the user to specify an initial and design state from a dict

[fwitte]

Just like the Network deserialization in Network.from_json/Network.from_dict there could be an equivalent implementation for the initial state or the design state.

A solution could be, that the user would specify init_state or design_state (will deprecate init_path and design_path) and it will be checked whether a python dict or a path to a json file is specified. Then the data are taken either by reading from the json file or directly from the dictionary.