- Make sure we clear out the group queue when we have a new VO that wants
  to halt the playing VO.
- Make sure we clear out all group queues when we stop all sounds.
Oops.
- A more GC-friendly way of clearing the queue.
- add support for stopping a sound group.
Merge pull request #325 from virtual-world-framework/sound-queue

Sound queue
Merge pull request #327 from virtual-world-framework/stop-sound-group

- add support for stopping a sound group.
Get queue delay working again.
Oops.