Add support for Facebook Watch

[selurvedu]

The videos can be watched without an account.

Popular videos: https://www.facebook.com/watch/ Live streams: https://www.facebook.com/watch/live/ Shows: https://www.facebook.com/watch/shows/

An example of a "Shows" channel: https://www.facebook.com/watch/790116571171209/

Random video examples:

https://www.facebook.com/MrBean/videos/a-bean-roll-mr-bean/820992928677644/ https://www.facebook.com/DiscoveryUK/videos/how-are-bamboo-steamers-made/369158624139905/ https://www.facebook.com/790116571171209/videos/887860541396811/

Valid domains are www.facebook.com and m.facebook.com .