Implement legacy image portion of the data model

This also makes use of the newly created input system

data/registry_model/interface.py

@@ -37,3 +37,16 @@ class RegistryDataInterface(object):
   @abstractmethod
   def create_manifest_label(self, manifest, key, value, source_type_name, media_type_name=None):
     """ Creates a label on the manifest with the given key and value. """
+
+  @abstractmethod
+  def get_legacy_images(self, repository_ref):
+    """
+    Returns an iterator of all the LegacyImage's defined in the matching repository.
+    """
+
+  @abstractmethod
+  def get_legacy_image(self, repository_ref, docker_image_id, include_parents=False):
+    """
+    Returns the matching LegacyImages under the matching repository, if any. If none,
+    returns None.
+    """