Refactor best bets interface

We built the best bets portion of search-admin with a focus on the bets themselves, when in fact it's a lot cleaner both from the interface and the code to deal primarily with queries, which have many bets (both best and worst).

This rebuilds the application with that perspective.

https://www.pivotaltracker.com/story/show/71583226
https://www.pivotaltracker.com/story/show/73054278

Additional tasks:
- [x] Add link to new query from queries index
- [x] Add link to CSV from queries index
- [x] Add query editing
- [x] Add query deletion
- [x] Add link to bet editing
- [x] List the worst bets on the query page
- [x] Change the new bet form to include "is_best" checkbox.
- [x] Disallow null position for bets in new bet form
- [x] Disallow negative or 0 position for bets in new bet form
- [x] Show the comment field for bets (both best and worst) in query page
- [x] Add a way back from a query page to the list of queries.