Refactor all stream extractor tests to use new base class.
Remove check if upload date is in the past: this does not have to hold true: youtube premieres turn up in search results even though they are in the future
- Handle special cases for languages where the number is not shown
- Rework the Downloader base implementation, allowing for more
advanced things to be done
- Separate the localization from the content country (just like
YouTube let's the user choose both).