Bring back and install System Administration category
Summary:
D22742 added the info KCM to the System Administration category, but that
category isn't actually shipped with System Settings. It only appears if you have
the systemd-kcm instatted, because it ships its own local version of that file (boo).
This patch makes System Settings ship the category itself. It will be removed from
systemd-kcm in D22930.
Test Plan:
Reviewers: VDG, GB_2
Reviewed By: VDG, GB_2
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22929