Create svg versions of kdf and kgraphviewer icons

@carlschwan @aacid Previews files were png files renamed to have svg extensions. The png files have been converted to SVG format. The kgraphviewer logo is very pixelated, so intent is not always clear. Can add these to the main code repositories first:

• https://invent.kde.org/utilities/kdf
• https://invent.kde.org/graphics/kgraphviewer for easier review if that would be helpful, but can also add them afterwards.