Commercial component - content API

This adds html and styling for the commercial component that is driven from DFP and uses the content API for it's content.

There is more work to be done on the DFP side to allow easier entry of chosen stories.

![screen shot 2014-08-14 at 15 20 18](https://cloud.githubusercontent.com/assets/1303616/3921152/7268d30c-23be-11e4-99d9-a92e271a5a54.png)

Sorry for the late review: please add an `alt` attribute