Due to Qt bug: https://bugreports.qt.io/browse/QTBUG-70138 (KDE bug:
https://bugs.kde.org/show_bug.cgi?id=401644) we have label opacity utterly failing
when the logout screen is superimposed over a bright background. Even though
QtRendering is the inferior renderer, this patch uses it as a workaround for the
aforemention bug since ugly (if it ever would be) text is better than (almost) no
text.