feat: add basic db handler, for tracking counter values

more to come i'm sure, this is all i need so far

tests/test_app.py

@@ -448,6 +448,15 @@ app_title = WuttaTest
         auth = self.app.get_auth_handler()
         self.assertIsInstance(auth, AuthHandler)
 
+    def test_get_db_handler(self):
+        try:
+            from wuttjamaican.db.handler import DatabaseHandler
+        except ImportError:
+            pytest.skip("test not relevant without sqlalchemy")
+
+        db = self.app.get_db_handler()
+        self.assertIsInstance(db, DatabaseHandler)
+
     def test_get_email_handler(self):
         from wuttjamaican.email import EmailHandler