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
this moves all the db model code behind an interface in prep for v2-2
Issue: https://coreosdev.atlassian.net/browse/QUAY-750
- [ ] It works!
- [ ] Comments provide sufficient explanations for the next contributor
- [ ] Tests cover changes and corner cases
- [ ] Follows Quay syntax patterns and format
