Improve QWidget KCM and QML KCM consistency
Summary:
- Set QWidget KCMs title font size to the same one as QML ones
- Add content margin to QWidget KCMs to match QML ones
- Only display own KCM title in QML case
Reviewers: mart, ngraham
Reviewed By: mart, ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22028