lxqt-config-monitor: Use QGuiApplication
lxqt-config-monitor: Use QGuiApplication

From the libkscreen v5.7(?), the KScreen::GetConfigOperation() does not
provide any outputs information if only the QCoreApplication is used.

lxde/lxqt-config,lxde/lxqt-config,lxde/lxqt-config,lxde/lxqt-config,stefonarch/lxqt-config,stefonarch/lxqt-config,stefonarch/lxqt-config