R1:c6125798542d

Add very basic routing to Nuance

Summary:
Ref T8783. Sort out some relationships and fields:

- Make Items 1:1 with Queues: each item is always in exactly one queue. Minor discussion on T8783. I think this is easier to understand and reason about (and implement!) and can't come up with any real cases where it isn't powerful enough.
- Remove "QueueItem", which allowed items to be in multiple queues at once.
- Remove "dateNuanced", which is equivalent to "dateCreated" in all cases.

Then add really…