Provide an option so that images that need to be upscaled are simply copied and given filename specified using naming convention

[hal-gh]

There may well be a logical workaround for this which I haven't thought of, so I welcome any suggestions.

However, for static code, like CSS, it's not possible to check the existance of an image in an if/then/else construct. Thus, for any images that would need to be upscaled to provide a file for larger media queries, it would be good to have an option that causes responsive-images to simply copy the file verbatim, and give it the respective responsive filename as per the options.

This is similar to #45, but I think createNoScaledImage:true solves that OP's issue.