[rt-users] Change queue with a scrip before ticket creation.

[Emmanuel Lacour]

Here we used the following method:

- an incoming queue without watchers, without anything except a scrip
  that dispatch tickets in others queues
- a fallback error queue with admins as watcher in case the dispatch
  cannot be done.
- a scrip that trigger on queue change in every queues except incoming
  queue to do usual oncreate things