Add functions in the Py wrapper: size(), get_factor(), save() and adapt the...

Add functions in the Py wrapper: size(), get_factor(), save() and adapt the constructor to read a Faust from file.

The FaustPy.Faust constructor is able to receive a matlab file as a Faust definition (saved before with FaustPy.Faust.save() or the Faust matlab wrapper).

Adding also needed functions in Py wrapper C++ backend (FaustCoreCpp): get_fact_nb_rows(), get_fact_nb_cols(), get_fact().
Adding a piece of code in quickstart.py for testing.