CSS customization on advent calendar

- add an extract on the list (I get the first paragraph via a twig ext)
- add a calendar in the author / info block
- reverse the list order, newer article first
- add pagination on top of all articles
- handle very long titles
- add snow in the header (yes this is mandatory)

Some screenshots:

![image](https://f.cloud.github.com/assets/225704/1621174/79cc73ba-5687-11e3-856e-99ee4137dbb4.png)

![image](https://f.cloud.github.com/assets/225704/1621179/8b562004-5687-11e3-9d3e-ba2bbb4f67e6.png)

![image](https://f.cloud.github.com/assets/225704/1621341/629a0fe6-568b-11e3-8161-a1786a27daf5.png)