Add new exemple with grouping widget + filter widget + childrow widget

First of all, very great job on this program.
I need to use grouping widget, filter widget and childrow widget together.
That's why I made the following changes.

I add an example in the documentation.

List of Changes :
Exclude group-header class in filter widget
Exclude cssChildRow class in grouping widget
Change calculation of colspan in grouping widget
Add !important for group-hidden class

![exemple](https://f.cloud.github.com/assets/5912646/1518047/2b9a809c-4b2e-11e3-8fc2-78f13c7cd25d.jpg)