Linked content cards experiments

- [new] Relative date
- [new] Precise type of content in card title ("related" or comment, video, gallery)
- [new] Rely on opengraph to fetch data, through a proxy located in `/cards/`

This does **not** cardify external links (but it's ready for it so it contains code that does it).

![screen shot 2013-08-16 at 16 37 51](https://f.cloud.github.com/assets/85783/976317/52fa3d46-068a-11e3-969d-c94e34652a86.PNG)

![Napoleon](http://24.media.tumblr.com/9a6fa1195265c72d27c41e52852fffde/tumblr_mhd4dlBBI51rqrt0mo1_500.gif)