3.0 add style to toolbar buttons

Ref to #260 .
Add a visual marker on the toolbar buttons. As I have no design skills I took the option to use the same color than the panel header. It allows to reflect the history mode state but I'm open to every other color choice. 

here's how it looks : 
![debugkit](https://cloud.githubusercontent.com/assets/4977112/4514993/2dc77d94-4b9f-11e4-9c71-c9fff74c3ce9.gif)

I updated it. I just wanted to save a selection but I think we don't really care here, it's one line less now.