Port desktoptheme, icons and workspace KCMs to SettingStateBinding
Summary: This depends on D27840.
Test Plan: Has been tested with the three modules mentioned in the commit message
Reviewers: crossi, hchain, meven, bport, davidedmundson, mart, ngraham, Frameworks, Plasma, VDG
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D27841