When a user leaves the room, after some configurable amount of time, remove their tracks from the queue

[override11]

Use Case:
User joins a room, and queues a whole playlist of tracks, then leaves with 1/2 of them remaining. There is currently no 'clean' way of cleaning all those out of the queue, other than skipping individual tracks. Maybe have a per-room configuration for this, so it can be set to a time limit or disabled entirely (keeping the current behavior)

[diginc]

I feel like this issue might fall under a more global feature that needs to be addressed: User ranks/permission (#85, #161) groups should exist with limits on queue additions to combat troll behavior or excessively long set list queuing.

Registered user queue limit: 1 song
Probation group queue limit: 0 song
All higher ranks (like 'Room Regular/DJ', 'Moderator', 'Room Owner') could all be configurable between 0-unlimited by the owner.