Automatically create subqueues on user registration

It'd be nice if users automatically had subqueues created on user registration. In particular, I have a handful of queues which every registered user needs. I could also foresee situations where this could be handy with modules like role_autoassign. Here's a first stab at that functionality.

There are a few other issues worth thinking about, like whether or not we should clean up existing queues if user roles change. I lean towards that being a setting.

Either way, patch introduces a setting on the queue creation/edit page, and creates applicable queues upon user registration.