[CORE-4293] Modified the db namespace

The db namespace now has the functionality to support the required
endpoints described in [CORE-4293], [CORE-4292] and [CORE-4314].
IN PROGRESS - issue CORE-4293: Notification Agent: Modify the
count-messages endpoint to return number of unreceived system messages. 
https://pods.iplantcollaborative.org/jira/browse/CORE-4293

The count-message endpoint not returns the total number of new
(unreceived) and the total number of unseen system messages.

The JSON document fields "total" and "total-system-messages were renamed
to "user-total" and "system-total", respectively.