Merged requested to merge work/davidre/qml into master
The settings are now read via KConfigXT, with a trick to follow the config scheme of SDDM. One KConfig object is used to read the defaults and another one to read the actual config values, see SddmSettingsBase.h for details. The UI is now entirely in Qml and follows the GridviewKCM style. The preview pane has been moved into a Dialog. The "Advanced" has been moved into a page called "Behavior" and the sync options live now in a OverlaySheet accessible from the main page as does the background configuration.