Add initial livefyre integration.

This include a new cambio.comment.js and some abstraction for handling
livefyre comments loading and collection switching to support ajax'd load
of articles.
Add event triggering behavior.
Final draft implementation that works on article overlay changes.

This currently hardcodes configuration for an unsigned usage of livefyre.
Ideally, we'll be changing this to use the signed approach but it's not
working for some reason.
Use signed request for livefyre request.