[RFC] player: set playlist title to media title if not set already

[christoph-heinrich]

The title in the playlist should get set when we get a title and the playlist title isn't set already.

Related #8548. Somewhat closes #4780, but still only shows titles for files/urls that have been opened before. I don't think we should make a bunch of requests just to get the titles.

I don't know if this is the right way of going about it.