Add PHPMetrics to “Who uses?”

I have created a specific logo since no one exists :-/.
Here is the final render:
![capture d ecran 2014-11-07 a 10 25 38](https://cloud.githubusercontent.com/assets/946104/4950821/346ad188-6660-11e4-81ba-a10d50a41a3d.png)
Are you ok?
Will fix https://github.com/hoaproject/W3/issues/9.

/cc @Halleck45