Sort services by newest created first

Other than which services are live it’s also interesting to know what
services are getting created on Notify. So let’s put the newest ones at
the top of the page.

tests/__init__.py

@@ -65,7 +65,8 @@ def service_json(
         'sms_sender': sms_sender,
         'research_mode': research_mode,
         'organisation': organisation,
-        'branding': branding
+        'branding': branding,
+        'created_at': str(datetime.utcnow())
     }