Use reference package internally

Most places in the registry were using string types to refer to
repository names. This changes them to use reference.Named, so the type
system can enforce validation of the naming rules.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

registry/storage/blobwriter.go

@@ -326,7 +326,7 @@ func (bw *blobWriter) moveBlob(ctx context.Context, desc distribution.Descriptor
 // resources are already not present, no error will be returned.
 func (bw *blobWriter) removeResources(ctx context.Context) error {
 	dataPath, err := pathFor(uploadDataPathSpec{
-		name: bw.blobStore.repository.Name(),
+		name: bw.blobStore.repository.Name().Name(),
 		id:   bw.id,
 	})