add stats panel, add number formatter

I've added a statistical facet panel which fits my needs (ie: total and mean for http request's bytes).

I also added a way to format numbers: '15,453,233,976 docs' is more readable than 15453233976 docs :)

The number filter use the angularjs one, it will benefit from the localisation module.
The metric filter is for base 10 (ie: 10M), the binary filter is for base 2 (ie 5 GiB)

![capture decran 2013-12-04 a 13 26 16](https://f.cloud.github.com/assets/2727570/1673043/650173d2-5cdf-11e3-8b82-4ac06ed96ddd.png)

![capture decran 2013-12-04 a 13 26 46](https://f.cloud.github.com/assets/2727570/1673045/6a10c5b2-5cdf-11e3-947e-14e8a3e744ba.png)