Fix form submission in Webkit

Summary:
In Firefox, the "change" event bubbles for DOM 1 handlers (i.e.
"onchange"), but in WebKit it only bubbles for DOM 2 handlers.

WebKit bug here: https://bugs.webkit.org/show_bug.cgi?id=24516

Where the form has multiple values, I registered the bubbling onchange
using a DOM 2 handler (jQuery uses it under the hood).  Where the form
contained only a select box, I just used the direct DOM 1 handler.

Test Plan:
I tested locally in Chrome and element changes caused the form to
submit.

Reviewers: joelburget, joel

Reviewed By: joel

Differential Revision: http://phabricator.khanacademy.org/D1012