plugins.youtube: Fake user agent on HLS streams.
plugins.youtube: Fake user agent on HLS streams.

Resolves #319.

chhe/livestreamer,wlerin/streamlink,javiercantero/streamlink,sbstp/streamlink,blxd/livestreamer,jtsymon/livestreamer,Klaudit/livestreamer,Masaz-/livestreamer,derrod/livestreamer,wolftankk/livestreamer,charmander/livestreamer,flijloku/livestreamer,gtmanfred/livestreamer,gravyboat/streamlink,back-to/streamlink,chhe/streamlink,bastimeyer/streamlink,mmetak/streamlink,caorong/livestreamer,beardypig/streamlink,okaywit/livestreamer,mmetak/streamlink,javiercantero/streamlink,streamlink/streamlink,lyhiving/livestreamer,Dobatymo/livestreamer,ethanhlc/streamlink,melmorabity/streamlink,jtsymon/livestreamer,derrod/livestreamer,programming086/livestreamer,charmander/livestreamer,Feverqwe/livestreamer,intact/livestreamer,chrippa/livestreamer,wolftankk/livestreamer,Saturn/livestreamer,blxd/livestreamer,intact/livestreamer,flijloku/livestreamer,beardypig/streamlink,ethanhlc/streamlink,back-to/streamlink,Klaudit/livestreamer,hmit/livestreamer,wlerin/streamlink,melmorabity/streamlink,chhe/streamlink,bastimeyer/streamlink,gtmanfred/livestreamer,chhe/livestreamer,streamlink/streamlink,sbstp/streamlink,Dobatymo/livestreamer,caorong/livestreamer,breunigs/livestreamer,programming086/livestreamer,Feverqwe/livestreamer,fishscene/streamlink,breunigs/livestreamer,chrippa/livestreamer,Masaz-/livestreamer,lyhiving/livestreamer,okaywit/livestreamer,fishscene/streamlink,hmit/livestreamer,gravyboat/streamlink,Saturn/livestreamer