Instantiate parameter factories once
Created by: stefanoborini
Backward incompatible change. Requires updating the plugins. Requires to specify the factory classes for the MCO parameters, instead of instantiating them every time.
Required changes to the plugins:
- a new method on the MCO factory get_parameter_factory_classes() must return the parameter factory classes.
- the current parameter_factories() method must be removed.
Fixes #135 (closed)