Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

* Combine verification and reverification photo submission end-points.
* Combine verification and reverification Backbone models.
* Allow deletion of verification status in Django admin.
* Initial verification from a checkpoint is associated with the checkpoint.
* Fix critical bug in which an invalid link was sent to Software Secure
  for the photo ID image of reverification attempts.