Queue classifications

Closes #48 
I think this is the biggest contention I have at the moment. 

The UserQueueSubject -> SetMemberSubject could be re-modelled as multiple instances of UserQueueSubject with a belongs_to SetMemberSubject. 

It would populate more UserQueueSubject entries but these are deleted after use (plus the use case wouldn't really define that many, i say this now though). Am i missing a trick with the way you've setup links, etc so that the FK's have to be an array / model record? 

Thoughts?