Display names, help text, and "deprecated" for Advanced Settings.

Hackathon with @frrrances and @mhoeber 

@dmitchell Please review the Python/JS code. Much of it should be familiar to you. :) Mark will be updating the user-visible Strings, but all functionality is working.

Depends on https://github.com/edx/XBlock/pull/223 (which has already been merged).
I was a little nervous about the performance of sortBy if it evaluated the key function each time it compare an item. Fortunately, it is smarter than that, and will only evaluate each key once per sort.