Django 1.8: Stop using deprecated models.get_models()
Django 1.8: Stop using deprecated models.get_models()

Warning was:
`RemovedInDjango19Warning: django.db.models.get_models is deprecated.`

This commit uses the new application loading system instead.

artefactual/archivematica-fpr-admin,artefactual/archivematica-fpr-admin,artefactual/archivematica-fpr-admin,artefactual/archivematica-fpr-admin