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 endpoint was implemented at /system/new-messages.  It works exactly.
like /system/unseen-messages and /system/messages.
CORE-4314 Added endpoint to mark a set of sys msgs as received
 
https://pods.iplantcollaborative.org/jira/browse/CORE-4314

The endpoint is at /system/received and behaves the same way as the
/system/seen endpoint excepting that it marks a messages as received
instead of seen.