feat(controller): add `deis certs:transfer` endpoint

[Cryptophobia]

From @sstarcher on September 28, 2016 16:19

Certificates are owned by the individual who creates them. If this person leaves the only option is to delete the cert and re-add the cert.

Originally requested from Deis v1 - https://github.com/deis/deis/issues/4576 Similar to app:transfer - https://github.com/deis/deis/pull/4193

Copied from original issue: deis/workflow#526

[Cryptophobia]

From @bacongobbler on September 28, 2016 16:36

For now most administrators have been handling this inside the container using https://deis.com/docs/workflow/troubleshooting/kubectl/:

kubectl --namespace=deis exec -it deis-controller-h6lk6 python manage.py shell
>>> from api.models import Certificate
>>> from django.contrib.auth.models import User
>>> newowner = User.objects.get(username='newowner')
>>> c = Certificate.objects.get(name='mycertname')
>>> c.owner = newowner
>>> c.save()

But I agree that having some form of god-mode visibility and transfer-ability for all resources (including certificates) through the API would be useful.