OPEN - issue CORE-4246: get all system messages endpoint needs to
indicate whether or not a message has already been seen 
https://pods.iplantcollaborative.org/jira/browse/CORE-4246

The /system/messages and /system/unseen-messages endpoints now return a
list of message records that indicate whether or not the user has
acknowledged the message.
OPEN - issue CORE-4246: get all system messages endpoint needs to
indicate whether or not a message has already been seen 
https://pods.iplantcollaborative.org/jira/browse/CORE-4246

fixed doc typos