Add a class to manage all ModelBuilder features

[MaximeMorille]

This class will contain all the public accesses to ModelBuilder features:

from braincube_connector import client

demo = client.get_instance()

study = demo.ModelBuilder.create_study()
studies = demo.ModelBuilder.all()
other_study = demo.ModelBuilder.get("some-uuid")

It will build the prefix of all ModelBuilder requests. Those requests are all beginning with /{version}/{braincube-name}.