SVG downloads in IE/Edge contain literal data URL

[radhikalism]

When using downloadImage to save a SVG snapshot via MS IE or Edge, the saved file contains the literal data URL value rather than the decoded SVG source code.

I believe this is a consequence of 22d902b before which url contained the raw SVG source. That commit is probably correct to only put URL values in url, but that means the URL should be decoded before constructing a Blob and saving as a file.

See my PR here for a fix: radhikalism#1

[alexcjohnson]

possibly related to (or duplicate of even) #699 ?

[bpostlethwaite]

cc @cldougl - looks like we have progress on this one