Fix appdata and correct a name mismatch

This subsumes !2302 (closed) and should also fix a bug I noticed with the GNOME packaging (not present in the snap) where the launchable name and actual application name don't match.

Once this gets merged, the INKSCAPE_1_0_1 tag should be moved to this commit and the new packages uploaded to all the relevant places, so finally Linux users can get a native Inkscape application that doesn't behave weirdly when they click on the icon.