Content Views Rework: filter updates for api consistency and to support CLI

This commit has a few minor updates to ensure api consistency, support
CLI and improve behavior such as:
- routes: use content view resource on filter index/create
- routes: do not use content view resource on filter show/update/delete
- only update filter parameter created_at if the filter have changed
- updates to docs to  support apipie bindings for hammer-cli-katello support
- ...
API V2: Built out content views and added tests
Content Views: Fixing uninitialized Repository test error
Merge pull request #3654 from daviddavis/cv-rework-api

Content Views: API V2 work and tests
Merge pull request #3660 from bbuckingham/cv-rework-filters

Content Views Rework: filter updates for api consistency and to support CLI
Content Views: Initial work to generate a content view prototype.
Content Views: Converting content view prototype to connect to API backend.