additional variants styling

- borders on top of sections instead of stories
![screen shot 2014-06-03 at 16 22 56](https://cloud.githubusercontent.com/assets/1492162/3162227/21e4811a-eb33-11e3-8100-5f8906d47f61.png)
- hide images for 3col1storiesThumb for tablet width and less
![screen shot 2014-06-03 at 16 27 07](https://cloud.githubusercontent.com/assets/1492162/3162266/8d343d5c-eb33-11e3-9416-ccbec4da0e5f.png)
![screen shot 2014-06-03 at 16 26 59](https://cloud.githubusercontent.com/assets/1492162/3162267/8d4754be-eb33-11e3-8ee8-6064c0bbeb18.png)
![screen shot 2014-06-03 at 16 26 38](https://cloud.githubusercontent.com/assets/1492162/3162268/8d49a14c-eb33-11e3-9a29-5f805d119528.png)