[WIP] Attempt to pickle model

[shuttle1987]

Closes the issue about model serialization #76

[shuttle1987]

Currently pickling fails with this error:

  File "/home/janis/persephone-web-API/pipfileenv/lib/python3.5/site-packages/connexion/decorators/decorator.py", line 44, in wrapper
    response = function(request)
  File "/home/janis/persephone-web-API/pipfileenv/lib/python3.5/site-packages/connexion/decorators/parameter.py", line 207, in wrapper
    return function(**kwargs)
  File "/home/janis/persephone-web-API/persephone_api/api_endpoints/model.py", line 98, in post
    models_storage_path=Path(flask.current_app.config['MODELS_PATH'])
  File "/home/janis/persephone-web-API/persephone_api/api_endpoints/model.py", line 46, in create_RNN_CTC_model
    pickle.dump(model, pickle_file, protocol=4)
TypeError: cannot serialize '_io.TextIOWrapper' object

[shuttle1987]

This PR may not end up being necessary when persephone-tools/persephone#197 is merged in the upstream Persephone library.