Change models.py to use typed class members instead of a list of strings.

tests/pending_manager_test.py

Index: tests/pending_manager_test.py
diff --git a/tests/pending_manager_test.py b/tests/pending_manager_test.py
index bd96c5d3bbb7dfd3b4ec9aeb4b40c4e25fab0204..d33b91b5fe61ad2d1058e8fb90c74793d30d266d 100755
--- a/tests/pending_manager_test.py
+++ b/tests/pending_manager_test.py
@@ -67,7 +67,6 @@ class TestPendingManager(mocks.TestCase):
         [])
     filename = os.path.join(self.root_dir, 'foo.json')
     empty = """{
-  "__persistent_module__": "pending_manager",
   "__persistent_type__": "PendingQueue",
   "pending_commits": []
 }