Backbone version of the course outline page

STUD-1726

Converted the course outline page to Backbone so as to support dynamic client-side updating.
We have to iterate in reverse because the ancestors are listed from closest to furthest away, i.e. subsection then section (and sometimes other xblocks in between too). The tree needs to be rendered from the top down, so we have to go in reverse order.

I'll add a comment to clarify this.

I'll