Default external downloader

[papadoc]

Pretty much all external downloaders have issues with certain files. At the very least, there needs to be another prompt to download through the built-in downloader if the download is declined in the external downloader. 

Aside from that, it'd be really great if we could specify to only use the external downloader for certain file extensions and/or only for downloads on certain specified sites.

[Admini]

Thanks for your suggestion.
We will consider it, but I think this may be a little complicated for the download feature.
This requires us to add another option "default external downloader", is that right?