feat: add table/model for app upgrades

tests/db/model/test_upgrades.py

@@ -0,0 +1,15 @@
+# -*- coding: utf-8; -*-
+
+from unittest import TestCase
+
+try:
+    from wuttjamaican.db.model import upgrades as mod
+except ImportError:
+    pass
+else:
+
+    class TestUpgrade(TestCase):
+
+        def test_str(self):
+            upgrade = mod.Upgrade(description="upgrade foo")
+            self.assertEqual(str(upgrade), "upgrade foo")