Problem Description: repositories cannot be created or updated in the current version of the automation hub UI

Proposed Solution: replace the existing Repositories in the "repository management" page, with a new page that allows users to view, update, delete and create repositories.

These new pages will use the existing pulp apis for managing repositories. A summary of the design can be found here: https://docs.google.com/document/d/18mS8wKDrrKrW7YDm1vfws2GrOPFkRWVWxuA5bn8FQ88/

Mockups: https://marvelapp.com/prototype/963i3bd/screen/87982049