Content cards

Creates an endpoint for article-embeds ( 'content cards' ) 
* Returns jsonified html / and actual html 
* Styles:

Examples

Review:
![review](https://cloud.githubusercontent.com/assets/986155/5033098/f1025b82-6b5a-11e4-94a8-82bfad548ac8.png)

Comment: 

![comment-card](https://cloud.githubusercontent.com/assets/986155/5033149/5e899544-6b5b-11e4-93f9-830f876e1514.png)



these cards only appear on content pages? so can't it go in `head.content.css` rather than `global`?