Occupancy Module

## Basic Feature: Occupancy Module Reorganization

We have a handful of different occupancy model classes in the `smart_control.simulator` module.

Let's move them all into a new `smart_control.simulator.occupancy` sub-module.

Let's make sure to update all references accordingly, and make sure tests are passing.

Finally, we should update the docs site so there is a single page for all the classes in the new occupancy module (moving them from their original locations and/or adding new docs entries as applicable).

## Bonus Feature: Occupancy Model Comparison Charts

It would be nice to also create a new script ("smart_control/simulator/occupancy/compare.py") to generate one or more charts and graphs that compare the results from all the different occupancy models.

At minimum if should create a plot of the occupancy over time. The plot should cover a single day in 5 minute step intervals, plotting current local timestamp (in "US/Pacific") on the x axis, and average occupancy on the y axis. A line chart is probably best, with one series for each of the occupancy models.

Let's save the plot (as PNG in the "docs/assets/images" directory, and as HTML in a new "docs/assets/plots" directory.

Finally, we should display the plot as a PNG image in the new occupancy docs page, and/or provide a link to the HTML plot as a separate page in the docs site.