Fix Appimage icon coloring
Following he recent changes to BreezeIcon and IconThemes frameworks, icon coloring is now broken in AppImage on Gnome Desktops. Apps with a dark color theme have dark icons, making them hard to use as can be seen in the latest Kate and Kdenlive Qt6 AppImages. This patch re-introduces the iconengine registering to handle svg files, fixing AppImage icons on Gnome Desktop.