ea5b999fc0
In support of making the storage API ready for supporting notifications and mirroring, we've begun the process of paring down the storage model. The process started by creating a central Registry interface. From there, the common name argument on the LayerService and ManifestService was factored into a Repository interface. The rest of the changes directly follow from this. An interface wishlist was added, suggesting a direction to take the registry package that should support the distribution project's future goals. As these objects move out of the storage package and we implement a Registry backed by the http client, these design choices will start getting validation. Signed-off-by: Stephen J Day <stephen.day@docker.com>