Port to QQC2 and FormLayout
Summary: No big visible changes, but simplifies and modernizes the code
Test Plan: used all functionality of the systray config dialog
Reviewers: Plasma, VDG, ngraham
Reviewed By: VDG, ngraham
Subscribers: ngraham, abetts, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D17212