ClinicExporter should use find_each

We don't want to load 4000+ objects into memory :panda_face:
Merge branch 'master' of github.com:mission-of-mercy/mission-of-mercy
Add PatientFlow to ClinicExporter

Also fix up ClinicExporter so it actually exports data
Styles and formatting for Clinic Exporter

- Format time data
- Bold and center header row
Merge remote-tracking branch 'upstream/master'