Summary:
kcmshell5 depends on plasma-workspace. By using our own tiny wrapper for opening the KCM we avoid pulling
in plasma-workspace and everything that comes with it on non-Plasma systems.

Test Plan: kdeconnect-settings shows the KCM

Reviewers: #kde_connect, sredman

Reviewed By: #kde_connect, sredman

Subscribers: sredman, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D17383