Config bits for appengine, require.js, requirements, etc.

Summary: Configuration files that bring everything together. I decide to use require.js to avoid lots of frustration from javascript poor dependency management. What is more it also allows asynchronous loading of dependencies in contrast to how browser would have done it. It's easy to replace it if necessary.

Reviewers: csilvers, alpert, joel

Reviewed By: alpert

CC: ben

Maniphest Tasks: T1210

Differential Revision: http://phabricator.khanacademy.org/D3016