Start KOrgac via DBus activation on launch

Summary:
KOrgac is autostarted on session start, but just to be sure, we also try to launch it
on Kontact (and KOrganizer) start via DBus invocation.

Reviewers: KDE PIM, vkrause

Reviewed By: KDE PIM, vkrause

Subscribers: kde-pim

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D29505