Add new Manifest, ManifestLabel, ManifestLegacyImage and ManifestBlob tables and start writing and GCing to/from them

This change also starts passing in the manifest interface, rather than the raw data, to the model for writing.

Note that this change does *not* backfill the existing rows in to the new tables; that will occur in a followup PR. The new columns in `tagmanifest` and `tagmanifestlabel` will be used to track the backfill, as it will occur in a worker.

data/model/repository.py

@@ -10,9 +10,10 @@ from data.model import (
   config, DataModelException, tag, db_transaction, storage, permission, _basequery)
 from data.database import ( 
   Repository, Namespace, RepositoryTag, Star, Image, ImageStorage, User, Visibility,
-  RepositoryPermission, RepositoryActionCount, Role, RepositoryAuthorizedEmail, TagManifest,
-  DerivedStorageForImage, Label, TagManifestLabel, db_for_update, get_epoch_timestamp,
-  db_random_func, db_concat_func, RepositorySearchScore, RepositoryKind, ApprTag)
+  RepositoryPermission, RepositoryActionCount, Role, RepositoryAuthorizedEmail,
+  DerivedStorageForImage, Label, db_for_update, get_epoch_timestamp,
+  db_random_func, db_concat_func, RepositorySearchScore, RepositoryKind, ApprTag,
+  ManifestLegacyImage, Manifest)
 from data.text import prefix_search
 from util.itertoolrecipes import take
 
@@ -275,6 +276,13 @@ def garbage_collect_repo(repo, extra_candidate_set=None, is_purge=False):
           logger.info('Could not GC derived images %s; will try again soon', image_ids_to_remove)
           return False
 
+      # Delete any legacy references to the images.
+      (ManifestLegacyImage
+       .delete()
+       .where(ManifestLegacyImage.image << image_ids_to_remove)
+       .execute())
+
+      # Delete the images themselves.
       try:
         Image.delete().where(Image.id << image_ids_to_remove).execute()
       except IntegrityError: