Features/business vertical

* Adds the new Business vertical template and a 'default' template which all other Verticals currently fall back to. 
* Adds a compound index to NewsStory for retrieving Marketplace articles based on 'marketplace' source
* Removes reverse-chron "Latest Headlines" Section for now from the main headline section since most Verticals have a blog by default
* Moves 'category/show' template contents into partials to be shared by default and business template
* Adds Jon's assets and styling

A couple questions:

Is there still a use case to leave "Latest Headlines" around?
Does the cache version need to be bumped?

Feedback on the second commit especially (3ab873d) would be much appreciated! Using the category slug to determine the template means we have to make sure each new vertical template has the same name as the category slug - which shouldn't be a problem since it won't happen often.