This is the same as the feature already present in the launcher and
connection settings. Not sure how much sense it makes for systemd services
as they run rather independently from the UI but maybe it is useful.
Apparently this is still problematic leading to errors like
`Qualifying with unknown namespace/class`. It seems that moving the enum to
a different header file works. The trick to use a macro to define
`enum class` ceased to work on the other hand.
Specifying a function with the namespace like
`void QtGui::FinalWizardPage::showResults()` leads to the same problem and
also needs to be avoided.
* Check directly whether changed properties contain a property
instead of checking indirectly whether the returned QVariant
is invalid.
* Avoid copying the QVariant.
* Effectively this should not change anything; the code is just
more readable and possibly more efficient.
Martchus