Make footer stick to bottom until content overflows

![2013-10-06 18_55_22-simon kjellberg](https://f.cloud.github.com/assets/173085/1277065/3789f56a-2ea8-11e3-9b5f-6e03d7ae4d92.png)
![2013-10-06 18_55_03-simon kjellberg](https://f.cloud.github.com/assets/173085/1277066/378a006e-2ea8-11e3-90fa-9871ad1eaf04.png)