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
Why'd you change the scope? That's a significant change. (Default scope is content) It changes where the field is persisted and what it means. I don't think you can do this.

Leave comma so it doesn't look like you changed the default.