Internalize subtitles downloading

This PR imports OROpenSubtitleDownloader along with its wrapper from MetaDataFetcherKit to ease future maintenance (#880 (closed)). Additionally, it addresses basic optimizations and simplifications.

changed milestone to %3.3.0

added 17 commits

• 83a951d5...98bab75f - 9 commits from branch videolan:master
• 6949d782 - Reachability: relocate to a newly created 'Imported' folder
• 319c26c4 - Import OROpenSubtitleDownloader
• a1481510 - Deploy internal OROpenSubtitleDownloader
• b47292c4 - Update MetaDataFetcherKit to avoid a conflict with the internal OROpenSubtitleDownloader
• b2c20ce6 - Add wrapper for subtitles downloader
• 70004000 - Subtitles downloader: simplify user agent handling
• 9e27bf98 - Subtitles downloader: privatise logging and fix typo
• 6234fe1f - Subtitles downloader: remove write-only variable and simplify

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approved this merge request

assigned to @jbk

added Feature label

merged

mentioned in issue #880 (closed)