Fronts story strip

Styling top stories 'strip'

Thoughts on this way of maintaing breakpoint definition in the CSS, but accessing from JS... (@kaelig, @phamann, @indeox)

https://github.com/guardian/frontend/compare/fronts-story-strip?expand=1#L2R2
https://github.com/guardian/frontend/compare/fronts-story-strip?expand=1#L1R32

![top-stories](https://f.cloud.github.com/assets/74132/1066989/43c9cdc6-13c0-11e3-92a6-a20ec02a4ef2.png)