youtube-dl: Update to 20190417

Changes:
version 2019.04.17

Extractors
* [openload] Randomize User-Agent (closes #20688)
+ [openload] Add support for oladblock domains (#20471)
* [adn] Fix subtitle extraction (#12724)
+ [aol] Add support for localized websites
+ [yahoo] Add support GYAO episode URLs
+ [yahoo] Add support for streaming.yahoo.co.jp (#5811, #7098)
+ [yahoo] Add support for gyao.yahoo.co.jp
* [aenetworks] Fix history topic extraction and extract more formats
+ [cbs] Extract smpte and vtt subtitles
+ [streamango] Add support for streamcherry.com (#20592)
+ [yourporn] Add support for sxyprn.com (#20646)
* [mgtv] Fix extraction (#20650)
* [linkedin:learning] Use urljoin for form action URL (#20431)
+ [gdc] Add support for kaltura embeds (#20575)
* [dispeak] Improve mp4 bitrate extraction
* [kaltura] Sanitize embed URLs
* [jwplatfom] Do not match manifest URLs (#20596)
* [aol] Restrict URL regular expression and improve format extraction
+ [tiktok] Add support for new URL schema (#20573)
+ [stv:player] Add support for player.stv.tv (#20586)

(leot)