Rviz pie chart

new rviz plugin: PieChart
see the image and [movie](http://youtu.be/kAKrJt_H1fM)

![screenshot from 2014-05-06 15 12 46](https://cloud.githubusercontent.com/assets/40454/2886437/4ca49822-d4e5-11e3-9111-2b27817cf271.png)