hello,

This patch adds a new interceptor for our shell packages.
Right now we cannot load an svg if the image is inside the /contents/images of the shell package.
So this patch solves that issue.

*Testing*
org.kde.desktop shell package works without any issue.

*Issues*

The interceptor doesn't return a scheme for the svg component.

PlasmaCore.SvgItem {
    svg: PlasmaCore.Svg {
        imagePath: "shellpackage:/images/bar.svgz"
    }
}

On the above code, the "path.scheme()" from the interceptor never returns
"shellpackage", so it is completely ignored.

But the following one it works

Image {
    source: "shellpackage:/images/foo.png"
}