create new ChangeSet API

src/c3nav/editor/models/changedobject.py

@@ -1,4 +1,5 @@
 import typing
+from collections import OrderedDict
 from itertools import chain
 
 from django.contrib.contenttypes.models import ContentType
@@ -284,3 +285,14 @@ class ChangedObject(models.Model):
 
     def __repr__(self):
         return '<ChangedObject #%s on ChangeSet #%s>' % (str(self.pk), str(self.changeset_id))
+
+    def serialize(self):
+        return OrderedDict((
+            ('type', self.model_class.__name__.lower()),
+            ('is_created', self.is_created),
+            ('is_deleted', self.deleted),
+            ('pk', self.obj_pk),
+            ('updated_fields', self.updated_fields),
+            ('m2m_added', self.m2m_added),
+            ('m2m_removed', self.m2m_removed),
+        ))