Backbone version of the course outline page

STUD-1726

Converted the course outline page to Backbone so as to support dynamic client-side updating.
The comment should say 'only expand the course and chapters initially' because the root of the tree is actually the course.

I'm not 100% sure why I have the this.renderedChildren boolean check there. I think this was an early attempt to preserve the expanded items, but I have a much more comprehensive solution now. I'll try taking it out...