Fully comment models.py

- require a category for every facility
3 jobs for 16-categories in 1 minute and 7 seconds
Status Job ID Name Coverage
  Test
passed #2948
whats-open-py2.7

00:01:03

passed #2949
whats-open-py3.5

00:01:06

passed #2950
whats-open-py3.6

00:01:07