[KCMs/Standard Actions] Give KCMShell window a sane default size
Summary:
BUG: 377653
FIXED-IN: 5.18.5
Test Plan:
Before:
After:
Reviewers: Plasma
Subscribers: cfeck, davidedmundson, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D26695