This is a patch to check if a user (or set of users) have an active Sakai session, ie if they are 'online'.
SAK-39896 Method to get most recent event time for a user
SAK-27335 Add online status widget
SAK-39468 Update SakaiCluster to check on SESSION_ACTIVE rather than waiting for session/locks to timeout
SAK-39602 ability to retrieve the time of an Event.
SAK-39463 Add USER_ID field to SAKAI_EVENT