Make code sticky on scrolling

For desktop you can see all the code even when you have a long chain of comments. Fixes partly #1926

![bildschirmfoto 2014-11-29 um 11 44 35](https://cloud.githubusercontent.com/assets/5362483/5234226/1f0bbe56-77bd-11e4-8083-d69a6ddf677e.PNG)