Scale articles above mobile

Ready for review, but please do not merge: tests do not pass (yet) on my local machine (something to do with a timeout).

This is a first step towards a better, more readable article page.

The CSS code is quite aggressive, it's on purpose: there will be much more stuff to debunk regarding grids later and this proof of concept does not deserve a deep architecture thinking.

We have two variants:
- Maximum width of 8 columns on tablets, then centered
- If viewport height is less than the desktop width, we float the main image (unless comments are ON, then we hide the image altogether)

![article-tablet](https://f.cloud.github.com/assets/85783/638554/58c27c6a-d2bf-11e2-8093-2a1361b5b00c.png)
![article-tablet-portrait](https://f.cloud.github.com/assets/85783/638556/5b95ad22-d2bf-11e2-91f0-8de7f554d28c.png)
![article-comments](https://f.cloud.github.com/assets/85783/638566/bd9e08f2-d2bf-11e2-9e67-776c49d4f9c9.png)