add an option to sort the stat panel results by label or value

![capture decran 2014-01-06 a 14 34 20](https://f.cloud.github.com/assets/2727570/1850597/4ad9c376-76d7-11e3-9012-3289cfcbaaf3.png)
![capture decran 2014-01-06 a 14 34 28](https://f.cloud.github.com/assets/2727570/1850599/4ce5b544-76d7-11e3-82b3-28e475384ee2.png)