KOrganizer: port from KRun::runCommand to KIO::CommandLauncherJob

Summary: Requires KF5 master, let me know if I should wait until landing

Test Plan:
Enabled Scheduling toolbar to start kaddressbook;
Went to the configuration dialog, custom pages, a button starts Qt designer.

Reviewers: mlaurent, winterz

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D28846