[npo] Add support for streams (Closes #4276)
[dvtv] Add support for playlists
[dvtv] Simplify
Merge branch 'petrkutalek-dvtv'
[dvtv] Fix thumbnail scheme
[yahoo] Improve video id detection (fixes #4521)
[yahoo] Replace two tests

The first one returned an internal server error.
The other doesn't seem to contain a video anymore.
[yahoo] Update extraction process

Their webpage uses now https://video.media.yql.yahoo.com/v1/video/sapi/streams/ for getting the video info.
[nerdcubed] Style fixes
[tmz] Fix test's thumbnail field
[rtp] Fix test's id field
[internetvideoarchive] Update test's duration field
[telecinco] Rename 'episode' group to 'id' in the _VALID_URL regex

MiTeleIE now uses '_match_id'
[dbtv] Make sure the 'id' field is a string
[extractor/common] Update docstring: replace FileDownloader with YoutubeDL