Add a beta ribbon on bottom right

This is to address issue #1841. I'm not really sure if this is what you want to have. I was wondering if the ribbon should be a link. At first I tried to position the ribbon on right top but this collides with the navbar (especially on mobile).

![bildschirmfoto 2014-11-03 um 18 10 30](https://cloud.githubusercontent.com/assets/5362483/4886536/30962070-637d-11e4-9c1c-be3e7f165d98.PNG)