[POC] Test application

This PR introduces a native test application which can be run using

````
./vendor/symfoiny-cmf/testing/bin/server
````

and accessed on `localhost:8000`

See demo:

http://cmf-menu.dantleech.com/app_test.php/render-test

I wonder if it wouldn't be neat to have a test application for each bundle, and the latest builds could be accesible on the web, e.g. cmf.menubundle.symfony.com or something.