Add data collector for the symfony web profiler

The last, but not the least :smile: 

![capture d ecran 2014-09-03 a 16 15 11](https://cloud.githubusercontent.com/assets/113045/4202899/db548e34-382b-11e4-8ebc-bbdecc228b8a.png)

I would rather name it ``pomm`` to avoid conflicts with other database bundles