Fully comment models.py

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

00:01:03

passed whats-open-py3.5 #2949

00:01:06

passed whats-open-py3.6 #2950

00:01:07