DO NOT MERGE  fixes #7705 - adding errata counts to content host details

This brings errata, repository association to errata, and applicable errata for systems into
the database. Also remove the Errata class that was based on Elasticsearch

TODO:

- [ ] fix bulk errata actions
- [ ] fix existing tests
- [ ] write lots of tests
:+1:

I'm wondering if we should indent this since it looks like git thinks it's a new file anyway.