Inject the tables metadata into the upgrade and downgrade functions. Fix a bunch of the downgrades to actually work.

util/collections.py

@@ -0,0 +1,12 @@
+class AttrDict(dict):
+  def __init__(self, *args, **kwargs):
+    super(AttrDict, self).__init__(*args, **kwargs)
+    self.__dict__ = self
+
+  @classmethod
+  def deep_copy(cls, attr_dict):
+    copy = AttrDict(attr_dict)
+    for key, value in copy.items():
+      if isinstance(value, AttrDict):
+        copy[key] = cls.deep_copy(value)
+    return copy