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Where does Unity (under 16.04) keep its list of desktop files for the Launcher. Not "where are .desktop files found?" but where are just the ones that Unity has right now in my launcher. One of them is placeholder "?" for an appimage executable, and I want to tweak that entry to point to an appropriate icon. The app doesn't have an existing .desktop entry yet in /usr/share/application or my .local stash, so I want to tweak the placeholder that Unity created for it rather than hand-roll one.