HLCM estimation notebook and simulation code

This is the code counterpart to #8

The HLCM segmentation variable was added to demographic_variables.py
The estimation notebook is HLCM Estimation.ipynb
The changes to simulation code are in models.py, lcm_utils.py, and Simulation.py
Note: lcm_utils.py is a portion of an upcoming open-source repo, so in the future we can import

SEMCOG / semcog_urbansim