Add support for className property with Single player imports

It looks like there is [no way](https://github.com/CookPete/react-player/blob/master/src/players/YouTube.js#L95) to provide className for YouTubePlayer

```html
            <YouTubePlayer
              className="youtube-player"
              url={video.uri}
              height={'100%'}
              width={'100%'}
            />
```