KCMs can be individually disabled by KIOSK if desired but wallpaper configuration cannot (unless you lock down
Plasma completely). Hence, at least honoring the ghns restriction here, until we have a proper solution
(that is a QtQuick equivalent of KNS3::Button).

Also, KNS3::DownloadDialog refuses to open when ghns is restricted *but* this applies only to using open()
or exec() but not a blatant show() we do from QML.

Differential Revision: https://phabricator.kde.org/D7086