[generic] Support data-video-url for YouTube embeds (Fixes #2862)
Add a duplicate check to /extractor/common.py playlist_result function
Add a _TEST_
Move duplicate check to generic.py
[README] Add thumbnail to _TEST example

While it's not mandatory, extractors are highly encouraged to provide a thumbnail field.
[playfm] Add extractor (Fixes #3538)
Merge remote-tracking branch 'origin/master'
Merge remote-tracking branch 'anovicecodemonkey/generic-data-video-url'

Conflicts:
	youtube_dl/extractor/generic.py
[YouTubeDL] Correct handling of age_limit = None in result
[generic] Simplify playlist support (#2948)