Content Views Rework: merging filters & filter rules, CRUD support

The following is a high-level summary of the changes:
1. Merge filter and filter rules together.  With these changes,
   there will be base filter class that the filter types will
   derive from (i.e. package, package group, erratum, puppet module).
   Each filter may have multiple 'parameters' associated with it.
2. Support elastic search indexing of filters
3. Provide v2 api support for CRUD (create/review/update/delete) actions

This commit does not address the following:
- Updates to content view publish/refresh to use the updated models
  (anticipate more changes needed  there)
- 'Green' tests

Both of the above will be addressed in separate commits.