Port KCalCore-related connect to PMF syntax

Summary:
This fixes the broken connects due to the KCalCore->KCalendarCore
renaming, which fixes clicking on dates in korganizer.

Test Plan: I can select dates in korganizer and the view updates! Magic!

Reviewers: vkrause

Reviewed By: vkrause

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D22838