Ordering in dropdowns

From @dianaclarke:

- [x] The items in the 'Day' drop-down aren't unique.  
       https://us.pycon.org/2015/admin/schedule/slot/add/
- [x] The items in the 'Slot' drop-down aren't unique.  
       https://us.pycon.org/2015/admin/schedule/slotroom/add/
- [x] The items in both the 'Day' and 'Slot' drop-downs aren't unique.  
      https://us.pycon.org/2015/admin/schedule/session/add/
- [x] The items in the 'Session' drop-down aren't sorted or unique.  
       https://us.pycon.org/2015/admin/schedule/sessionrole/add/
- [x] The 'Additional Speakers' items aren't sorted.  
       https://us.pycon.org/2015/admin/schedule/presentation/add/
- [x] The items in the 'Speakers' drop-down aren't sorted.  
       https://us.pycon.org/2015/admin/schedule/presentation/add/  
- [x] The items in the 'Proposal base' drop-down aren't sorted.  
       https://us.pycon.org/2015/admin/schedule/presentation/add/
- [x] The items in the 'Slot' drop-down aren't sorted.  
       https://us.pycon.org/2015/admin/schedule/presentation/add/
- [x] The items in the 'Speaker' drop-down aren't sorted.  
       https://us.pycon.org/2015/admin/pycon/pyconopenspaceproposal/849/
- [x] The items in the 'Category' drop-down aren't sorted.  
       https://us.pycon.org/2015/admin/pycon/pyconopenspaceproposal/849/