Add KQuickManagedConfigModule::mainUiReady signal
Useful when initialization needs the mainUi to access window and more.
Will be needed to implement the wallpaper kcm: https://phabricator.kde.org/T12622
Useful when initialization needs the mainUi to access window and more.
Will be needed to implement the wallpaper kcm: https://phabricator.kde.org/T12622