Pickling of CMF subclasses

[UriKH]

• Scenario: saving a CMF as pickle file and trying to use its __repr__.
• Issue: Missing properties
• Assumed source point of failure: CMF implements __getstate__ with matrices only and subclasses don't override.
• Proposed solution:

1. Remove usage of the __getstate__
2. Instead of using properties which shouldn't be saved in pickle, use @cached_property.
3. Override @cached_property such that cached properties will not be saved in pickle.

i.e. something like this maybe :)

def cached_property(func, ignore_pickle=True):
    prop = functools.cached_property(func)
    prop._ignore_pickle = ignore_pickle
    return prop

[RotemKalisch]

Fixed in #143

[RotemKalisch]

Also #152