Integration with Behat UI/API test code

My tests work now (though still a few outstanding mysteries).  I added an extension that generates a twig-based report.  

Re-run composer! as there are few more extensions to install. 

To run headless for UI tests, run with phantomjs profile (some Goutte issues I will go through).  

bin/behat -p phantomjs --config test/behat.yml --suite=transformcore_app.
This generated file should not be committed. Also, can we move it to to `test/build/` directory - then it will be git ignored.