stack vertically  keyboard shortcut on narrow viewport.


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Should help for #7319   
![capture d ecran 2014-12-26 a 19 08 39](https://cloud.githubusercontent.com/assets/335567/5558743/e7ff050e-8d32-11e4-84ec-546267632b79.png)
![capture d ecran 2014-12-26 a 19 08 46](https://cloud.githubusercontent.com/assets/335567/5558744/e8058564-8d32-11e4-9a9d-cd689c34304d.png)