added the SensioLabs security checker
feature #149 added the SensioLabs security checker (fabpot)

This PR was merged into the 3.0.x-dev branch.

Discussion
----------

added the SensioLabs security checker

Usage:

```
./app/console security:check
```

![screenshot](https://cloud.githubusercontent.com/assets/47313/3634555/80738bd2-0f36-11e4-92d3-890adfb89882.png)

![screenshot](https://cloud.githubusercontent.com/assets/47313/3634556/90f38c6e-0f36-11e4-82d6-cdf5bdfbd1bd.png)

Commits
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b280840 added the SensioLabs security checker