Option to retry media downloads on error

[fraganator]

When the download metadata and media function completes, it will notify the user of any images which it failed to download. This has proven very helpful in tracking and re-downloading media missed during the download process (due to internet dropouts, wifi issues, etc).

What would make this feature even better is a retry option, where LaunchBox will attempt to download just those images in the error list, and place them in the correct location with the correct filename.