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.
If these are dev/test requirements, they should go in the `require-dev` section. Also, can we pick a major release? e.g. `1.*`?

```
"guzzlehttp/guzzle": "*",
"phpunit/phpunit": "*",
"phpunit/dbunit": "*",
"chartinger/behat-twig-report-extension": "*@dev"
```