Add active, link, visited, negative, neutral and positive background colors
Summary: These colors were added to Kirigami and qqc2-desktop-style, so I had to add them here too.
Reviewers: Kirigami, Plasma, mart
Reviewed By: Kirigami, Plasma, mart
Subscribers: plasma-devel
Differential Revision: https://phabricator.kde.org/D26746