Superusers were getting confused because the users/orgs were being disabled and renamed, but still appeared in the list until they were GCed by the background worker. Now we just hide them.
Fixes https://jira.coreos.com/browse/QUAY-936
This could result in "hanging" robot accounts, although that would only leak the names of said accounts. Now we delete them immediately AND we proactively delete them before replacing the namespace (just to be sure)
Instead of deleting a namespace synchronously as before, we now mark the namespace for deletion, disable it, and rename it. A worker then comes along and deletes the namespace in the background. This results in a *significantly* better user experience, as the namespace deletion operation now "completes" in under a second, where before it could take 10s of minutes at the worse.
Fixes https://jira.coreos.com/browse/QUAY-838
