Feature: Clean client removal

[TuuLe3007]

Right now the server just says "Disconnecting client" when a client disconnects, and we wouldn't know who disconnected. If we add another message type (e.g goodbye_msg), and get the client to send the message to the server when they leave, then we can display their name in the console (and maybe send them their current standing on the leaderboard). If the client doesn't want to send the goodbye message and just sneakily leaves, the server can still handle it like right now.

[malensek]

Since we now have a linked list of active users, this should also remove the user from the linked list.

[malensek]

Update: while the goodbye message is a good idea, currently we don't even detect when a user leaves and update the list... So, that'd be a good place to start.