[universcience] Add new extractor

[flatgreen]

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What is the purpose of your pull request?

• Bug fix
• New extractor
• New feature

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Description of your pull request and other information

This is an extractor for a french science videos site : universcience.tv

example

[dstftw]

.* at border does not make any sense. With \d* you allow empty match. Using default implies non fatal. What is the point of 'None' string for default?

[flatgreen]

Here the new version. I followed your advice (thank you). Regexp is always a work in progress (for me !).
Tell me if it suits you.

[dstftw]

Irrelevant to this PR.

[flatgreen]

OK, the "import" is irrelevant.
I don't understand the 're.sub'. I believe the ytdl function is more efficient (?).

[TRox1972]

@flatgreen The line @dstftw mentions removes anything matching \d* x \d* from media_label, so instead just use re.sub like this: re.sub(' \d* x \d*', '', media_label).

[flatgreen]

string manipulation vs extraction. @TRox1972, @dstftw : Thank you

Here the new version.