quick script to compute the most frequent answers for each question

Summary:
We've had various ways to compute this, but I wanted to try
Bieber's new entity_loader out.  It gives you some fresh data (albeit
in a primitive format), as well as a simple script in Pure Python
that you can easily extend if/as you see fit.

Test Plan: none.  (blush)

Reviewers: eater

Reviewed By: eater

CC: davidbieber, alex

Differential Revision: http://phabricator.khanacademy.org/D3815