[Bugfix] prevent duplicate videos from being downloaded if the video's name changes (#396)

* Added methods for deleting outdated files

* Hooked up outdated file deletion to media download worker

test/support/files/subtitle.srt

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+Welcome to the Example Subtitle File!
+
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+This is a demonstration of SRT subtitles.
+
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+You can use SRT files to add subtitles to your videos.
+
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+Each subtitle entry consists of a number, a timecode,
+and the subtitle text.
+
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+The timecode format is hours:minutes:seconds,milliseconds.
+
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+You can adjust the timing to match your video.
+
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+Make sure the subtitle text is clear and readable.
+
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+And that's how you create an SRT subtitle file!
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+Enjoy adding subtitles to your videos!