Providers: Clean-up backend usage of providers.
While working on the new Products UI, we came to the realization that Providers serve as nothing more than a tag for a set of products. Currently our backend models for Products and Repositories rely heavily on the Provider model. The Provider model should be re-evaluated to determine it's current user stories and code re-factored to meet these requirements.
Imported from https://trello.com/c/DYfNUExf/213-providers-clean-up-backend-usage-of-providers_