[extractor/24tv.ua] Add extractors

[coletdjnz]

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Fixes #4287

Adds support for 24tv's custom video embed.

I also added support for extracting embeds from articles. Sometimes the iframe embeds are url encoded and stored within an html attribute, but would otherwise be able to be extracted via generic. To make this work I extract the url encoded HTML iframe, decode it, then return it back to generic via a data url. It is a bit hacky but I'm not sure what other way would be best to do this.

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