bloated model serialization

[hacktuarial]

The model object includes lots of bloat, e.g the full training data. It would be nice to serialize a minimal version containing only that which is necessary to make predictions.

Here's a tentative list of attributes needed:

• num_main
• effects
• groupings
• results_dict (nice to have)
• main_map
• main_effects
• inter_maps
• level_maps