Isolate BluePyMM from BluePyOpt using API provided by user

To allow for easier testing of the e-models provided, and to simplify the bluepymm main code, we should remove the bluepyopt specific code from the bluepymm core, and let the user implement an API to interact with the model.
Example of api functions (names are crazy of course):
create_hoc_for_parameters
run_model_and_return_score_for_certain_morphology

We probably should add a submodule to bluepymm to provide an example of such an API that can be adapted for user specific needs if necessary.