Adding independent scroll for sidebar and content.

Style tweaks to the sidebar
Here are screenshots for it
![custom](https://cloud.githubusercontent.com/assets/1457701/5564751/313dc2f0-8ea0-11e4-8203-64a4d19f2a47.png)
![default](https://cloud.githubusercontent.com/assets/1457701/5564750/313db6a2-8ea0-11e4-9bd8-ed17a24fcd72.png)