[potd] Modernize configuration settings
This patch replaces the ColumnLayout with Kirigami.FormLayout and make use of twinFormLayouts to link child layout with parent layout.
QQC1 comboboxes are retained due to a QQC2 bug with resizing the popup to delegate width.
Reviewed By: VDG, ngraham
Subscribers: abetts, davidedmundson, plasma-devel
Maniphest Tasks: T10586
Differential Revision: https://phabricator.kde.org/D20969