IN PROGRESS - issue CORE-4126: Add system message display area to DE. 
https://pods.iplantcollaborative.org/jira/browse/CORE-4126

Adapted the system_notification_acknowledgments entity to the schema
change to support user acknowledgment state tracking.  Since this is a
breaking change, the project version was increased.
BUG FIX users entity definition

The users entity definition now correctly references the
system_notification_acknowledgments entity.