Notifications when people leave post-game chat (long overdue!)

Nantes

This has been suggested for years, and I even recall a BHVR person saying that the notifications could not be implemented before because connections were peer-to-peer. They have been dedicated servers for well over a year now, so it's about time we get a notification when people leave the post-game lobby so we don't keep talking to the walls. Imagine how many collective hours are wasted in this way every week!