KCM: Fix connection list background and padding
Summary: Like D27379 the ListView in the Network Management KCM is incorrectly anchored to its parent ScrollView. This removes the anchoring, removing overlap of the scrollbar. In addition, it corrects the ScrollView's background so it actually displays correctly.
Reviewers: jgrulich!, Plasma, davidedmundson
Reviewed By: Plasma, davidedmundson
Differential Revision: https://phabricator.kde.org/D27382