Minification process for javascript

Summary: Add minification build. Only minified file gets uploaded to production. We cannot load jquery from CDN on shim based config. It's a limitation of require.js. This way we only get minified file and require.js on the server. I think I have not messed up deployment and everything works.

Test Plan: deploy and see if it works (don't change default!)

Reviewers: alpert, joel

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D3076