Fix pasting SVG as vectors on Windows

On Windows, inkscape puts the following mimetypes on the clipboard:

"image/x-inkscape-svg"
"application/x-qt-windows-mime;value=\"PNG\"" "application/x-qt-image"

While krita expected

"image/svg+xml"

Now we just look through all formats to see whether there's one htat
says 'svg' and then use that data.