qtxdg-mat: Rework exit codes
qtxdg-mat: Rework exit codes

An asked --help must return EXIT_SUCCESS.
Any option passed to an non existent module must return EXIT_FAILURE.

lxde/libqtxdg,lxde/libqtxdg,libqtxdg/libqtxdg,libqtxdg/libqtxdg