- session_(dla|action) is stored in egw_access_log table
- notifications refresh via ajax set notification_heartbeat timestamp in egw_access_log
- if notification_heartbeat is set (happens only for browser sessions with popup notification) sessions get removed from session list one minute after browser is closed
- new static method egw_session::notifications_active($account_id) to check if given user has an open browser with notifications popup checking, to ensure popup notifications can fall back to email
--> REQUIRES DATABASE UPDATE / SETUP