Add support for image plugin when no JS

[victorbjorklund]

I noticed that if you turn off JS for a page containing images using the image plugin it won't work:

(From https://nicholasreese.com/that uses elderjs image plugin)

But if we do the same with a site that uses gatsby image plugin it works:

(From https://gatsby-image-v2.surge.sh/ that uses gatsby image plugin)

I don't really know how we could achieve the same as gatsby but at least it seems possible.