Certificates: Add regeneration command

* Adds regenerate_user command, which lets you run certificates for one
  particular user in one particular class, regardless of whether they
  have a pre-existing certificate.
Add isoTime js view.
Video modul changes
Add new python field.
Refactor js.
Add js unit tests.
Add comment.
Update IsoTIme to be timedelta and update tests.
Add tests fro IsoTime methods.
Fix acceptance test.
Add test for IsoTime
Rename IsoTime to RelativeTime.
Changed help text for start and end time.
Fix typo.
Fix typo.
Fix typo
Change str of RelativeTime.
Fix to_json of RelativeTime to support Isotime format.
Fix checking exception message.
Update variable names and fix typo.