Port away from serviceOwnerChanged signal
Summary:
Use QDBusServiceWatcher::service(Un)registered signals, since in
most cases we only need to see one or the other, rarely both and
we basically never want to execute the same code for both.
Reviewers: vkrause
Reviewed By: vkrause
Subscribers: kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D26282