Use Youtube-dl for video downloads

A few of the rippers overlap with Youtube-dl.

It would be interesting to provide a "Youtube-dl ripper" that would use youtube-dl as the downloader for all the websites it supports, as well as serve as a backend to download videos for other rippers.

This would make updating some rippers with website changes much easier, as youtube-dl has a lot of contributors and is updated pretty quickly.

The easiest way I could see would be to use Jython to invoke youtube-dl, as outlined in the Jython book.

Another potential way would be to use the system's youtube-dl, but then we'd have to parse its output, which isn't standardized.

Obviously, this would be a pretty substantial undertaking, but I think it's interesting to at least discuss the idea, as it would make some rippers much easier to maintain in the long term and add support for a whole bunch of websites in one go.