Admin user 'admin' missing.

Created by: hixi

https://sentry.dev.njo.ch/geometalab/osmaxx-dev/group/13/

DoesNotExist: User matching query does not exist.
  File "osmaxx/excerptexport/views.py", line 142, in get_admin_user_or_none
    return User.objects.get(username=admin_user_name)