Disable the module if the setting is locked down
Summary:
In this case we simply disable the whole module since it manages only a
single key really. We could go finer grained allowing to add/remove
themes, but it'd be pointless really (and also removal has a side
effect on the selected theme anyway).
Reviewers: Plasma, mart
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D24699