Have table call onChange

Summary:
Most components call onChange when they are interacted with, this
didn't. toJSON seemed like an appropriate thing to return, as it
contains all the important info.

Test Plan:
* Add a console.log to onChange
* or wait for a separate commit

Reviewers: jack, alex

Reviewed By: jack, alex

Subscribers: alpert

Differential Revision: http://phabricator.khanacademy.org/D7174