PoC for model_builder to work with scikit-learn. (#161)

* Initial draft of version of model_builder to work with scikit-learn

* Run pre-commit checks and eliminate mutable default args to LinearModel.__init__

* Move default constructor parameters to properties

This avoids issues with mutable objects as default parameters.
It allows users to start from the default parameters and modify parts of
them before passing them to __init__.

* Add dimension names to model and fix bug in predict_proba

* black reformatting

Author: pdb5627