Promoted reviews

New promoted reviews widget. Depending on configuration, this will either append average score and link to the hcard, or pull the full text of all reviews into the body of the widget.

It's pretty likely that this will often end up getting pulled into the same page twice, each with different configurations... once in "aside before main" and again in "main". That's why there's the big if block in  show.html and in the top of show.coffee.js