Use org.kde.kcmutils/org.kde.config instead of kquickcontroladdons

This way, we do not use KDeclarative, but the QML plugin provided by the
relevant frameworks.
Using the KAuthorized API also has the advantage, that we can call a
method returning a boolean instead of a QStringList where we need to
check the length later on.

Depends on frameworks/kconfig!198 and frameworks/kcmutils!146