Fix delete application.

This (simplified) code does not work:

def delete(self):
    self.applicant.delete()
    super(Application, self).delete()

As deleting the applicant will delete the application, resulting in the
application delete failing.

Fixed by deleting orphaned applications in daily cron job.

Change-Id: Icf21cbe327e796f8aad792061e1ceab505e79a76