Queue classifications

Closes #48 
It's a style point so it doesn't really matter but you can totally write that conditional branching like

``` ruby
case
when params[:sort] == 'random' && params.has_key?(:workflow_id)
  random_subjects
when params[:sort] == 'queued' && params.has_key?(:workflow_id)
  queued_subjects
when params.has_key?(:subject_set_id)
  query_subject_sets
else
  query_subjects
end
```