Request to merge content-filters branch to master

This PR contains a fairly complete implementation of content view definition filters.

Things implemented
1) CRUD filters via UI or CLI to content view definition (CVD)
2) CRUD to for filter rules  for Package, PackageGroup, Errata via UI (CLI coming soon)
3) CVD publish now uses the filters to filter things accordingly.

Things to do 
1) Add cli implementation to create/delete filter rules 
2) Fix some cli inconsistencies (use filter id vs name)
3) Get filters to work with the "refresh" operation.