Port AgentManager away from deprecated serviceOwnerChanged signal

Authored by dvratil on Dec 29 2019, 1:51 PM.

Description

Port AgentManager away from deprecated serviceOwnerChanged signal

Test Plan: Akonadi and all agents start and operate as expected

Reviewers: KDE PIM, vkrause

Reviewed By: KDE PIM, vkrause

Subscribers: kde-pim

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D26274