[youtube] Extract additional meta data from video description on youtube music videos
YouTube music videos often have auto-generated video descriptions that can be
utilized to extract additional information about the video. This is desirable
in order to provide the user with as much meta data as possible. This commit
adds extraction methods for the following fields for youtube music videos:
- artist (fallback extraction methods added)
- track (fallback extraction methods added)
- album (new in this commit)
- release_date (new in this commit)
- release_year (new in this commit)
4 tests have been added to test this new functionality:
- YoutubeIE tests 27, 28, 29, and 30