Fix flatpak build
    
    The main package is a host service and does not belong in a flatpak; the
    applet and config app talk to the service over D-Bus.  They all do have
    a hard direct dependency on python3-firewall though.
    
    configure accepts an argument for the systemd unit installation
    directory, but not for the RPM macros, which therefore need to be moved.
    Some sources also have hardcoded /usr prefixes which need to be fixed.
    
    Like python3-qt5, pyqt6 also has a -base subpackage, which is all the
    applet needs.
    
    Also, byte-compile the gtk3 helpers used by firewall-config.