Introduce browser-less testing in the tutorial

[tarekoraby]

We should consider introducing the new TestBench browser-less testing (aka UI Unit Testing) in the tutorial. The latter now only covers:

• Unit and Integration testing in general, without covering the possibility of UI unit testing
• End-to-end testing (or browser-based testing)

Given the speed and reliability of browser-less testing, we should also consider mentioning it in the tutorial.