Migrate wallpaper config UI to Qt Quick Controls 2 and Kirigami
Summary:
KCM UI is gradually moving to Qt Quick Controls 2 components and Kirigami form layout. This can solve some layout consistency issue and HiDPI rendering issue (QQC1 doesn't render properly in HiDPI screen).
Reviewers: Marble, Plasma, ngraham
Reviewed By: ngraham
Subscribers: ngraham, marble-devel, kde-edu
Differential Revision: https://phabricator.kde.org/D25474