add packagestructure for KWin/Decoration
Summary:
use a KPackage/PackageStructure for aurorae themes as well
Patch by Demitrius Belai
Reviewers: Plasma, graesslin
Reviewed By: Plasma, graesslin
Subscribers: graesslin, plasma-devel, kwin, KWin
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D4974