show video controls for all youtube videos

TNL-184
@waheedahmed @symbolist @adampalay 
fix: Video controls of all videos after a private video do not show

Please put `section.video-controls` selector into `CSS_CLASS_NAMES` dict.
Also I'd suggest to use `visible` property to check if controls are visible:
```python
return self.q(css=CSS_CLASS_NAMES['controls']).visible
```