play and pause tests for youtube

That is draft for issue #1245 and is incomplete, but I wanted to have some feedback from the team, before continuing work on that task.

Some general questions:
1. Where this test should live? Maybe it's worth to move to browser tests?
2. Where should I land YoutubePlayer region?
3. I am not sure that it's possible to interact with video controls, they supposed to be provided by Gecko itself.
4. Because of p.3 I am not sure that it's possible to verify last step in moztrap case for this test.