Transparent sidebar, like the chat box

This patch makes the sidebar look like this:

![image](https://f.cloud.github.com/assets/198225/144075/76f32fa0-73eb-11e2-8612-c1e794493504.png)

This changes quite a few values in the css, so it will make the sidebar look different even if the plugin is not updated:

![image](https://f.cloud.github.com/assets/198225/144091/f9fc9afc-73ec-11e2-88cc-1ba8c2b921cb.png)

However it degrades quite nicely, IMO.