Integrate the driver testsuite

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Even though all the driver logic is actually inherited from MinkBrowserKitDriver, it could be interesting to run the driver testsuite on this repo as well. This could also allow detecting mistakes in WUnit itself (if they don't implement the HttpKernel/BrowserKit integration properly) as we know that MinkBrowserKitDriver works fine.

See https://github.com/minkphp/Mink/tree/master/driver-testsuite for the way to use this testsuite and https://github.com/minkphp/MinkBrowserKitDriver/tree/master/tests for the way BrowserKitDriver does to avoid relying on a webserver being running

[stof]

@patrickdreyer it would be great if you could work on this, as you might know better than me how to create a Yii app doing the rendering of the fixtures