Trivial stylistic refactoring.
Fix bug with unicode display of patients in admin.
Create reversion history for changes to the Patients app.

Use Django-Reversion[1], which adds a custom admin subclass that includes
the ability to see all previous versions of an object and revert to them.

[1] https://github.com/etianen/django-reversion
Merging Reversion tracking. refs #56