Add ability to cancel/blacklist download

[ghost]

For some reason, my downloader keeps downloading the same links which are bad because they link to Twitch streamers and youtube channels and downloader starts downloading them. I can provide a video if needed.

I would like to have a blacklist of downloads or the ability to cancel downloads.

[shadowmoose]

I agree that this is a good idea. The latest RMD release supports disabling retries, but that doesn't always solve the issue.