Add support for BDD testing

[stefandoorn]

I assume many have issues getting Behat including Selenium setup properly on their systems locally or on a Vagrant/Docker environment. It would be great to have a development Docker setup which runs similar tasks as being done on Travis (phpunit, phpspec, Behat, etc.) to allow smoother start of developing. When I started I found it rather hard to get it working. Would be great to have such functionality.