Webfont headline medium in articles

- Use correct headline serif font in articles on tablet (see screenshot)
- Abstract media query logic
- Use medium for bold, and semibold for bolder weights
- Include reduced version of the semibold headline font

![screen shot 2013-07-11 at 17 14 34](https://f.cloud.github.com/assets/85783/782975/02b4e54a-ea45-11e2-9d02-e4a550c5b4db.PNG)

![Boom](http://i.imgur.com/UA3XKTA.gif)