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* [gaskrank] Add new extractor

* [gaskrank] Add new extractor - fixes as requested

* [gaskrank] Add new extractor - style fix

* [Gaskrank] Add new extractor - requested fixes

* [Gaskrank] Add new extractor - fix md5 checksum

* [gaskrank] Add new extractor - more requested fixes

* [Gaskrank] Add new extractor - fixed all but one quantified code issues

* [Gaskrank] add new extractor - more fields extracted, added second test

* [Gaskrank] Add new extractor - requested fixes.

* [Gaskrank] Add new extractor - requested changes.

* [Gaskrank] Add new extractor - final(?) fixes.

Closes #11727

The heuristic is from #11724

Since Python 3.6, invalid escape sequences are deprecated. It's likely
that there are invalid escape sequences somewhere on the webpage, so
instead of unescaping the whole webpage, just unescape the URL.

See https://bugs.python.org/issue27364. That change was designed for
string literals, while it affects the 'unicode_escape' encoding as well.
The code path is:

str.decode('unicode_escape')
    codecs.unicode_escape_decode()
        PyUnicode_DecodeUnicodeEscape()

Example link (video in blocked group):
https://vk.com/search?c%5Bq%5D=%D0%9F%D1%80%D1%8B%D0%B6%D0%BE%D0%BA%20c%20%D0%BA%D1%80%D0%B0%D0%BD%D0%B0%20%D0%B2%20%D1%81%D1%82%D0%B8%D0%BB%D0%B5%20%D0%A7%D0%B5%D0%BB%D0%BE%D0%B2%D0%B5%D0%BA%D0%B0-%D0%BF%D0%B0%D1%83%D0%BA%D0%B0&c%5Bsection%5D=video&c%5Bsort%5D=2&z=video-10639516_456240611

[turner] fix downloading of secure hls formats using ffmpeg(closes #11358)(closes #11373)(closes #11800)

Covered by generic extractor

New parameter --playlist-random to randomize playlist download order. Fixes #11889