A scan for whether the video has been already been uploaded

[prototyperspective]

Please search Commons for the YouTube video ID before upload so people don't reupload already existing videos by accident.

This would also better enable completing only partially imported sets (e.g. if 42 videos of a channel have been imported but it has 50 useful ones) and eliminate the need to search Commons for long which often fails to show the existing video because it may have issues with the title. One could make it so that one could upload even if it detected it to be a duplicate but at least showing the user that and where the existing video or audio file is would be very useful.

This can be done with an insource search for the ID (set filetype to audio or video or use special search in the GUI): example.

This is related to #214 Note that in the Commons upload when uploading images it also checks whether the same image has already been uploaded and there is a speedy delete reason for duplicate files.