ColorSet concept in Theme
Summary:
Theme is now an attached property rather than a singleton (in 2.2 import)
a "colorSet" property can be defined on it and all its color properties
will change to that given set (which follows KColorScheme ColorSet)
all child items will inherit the theme of ancestor objects, until instructed not to
Test Plan: Kirigami Gallery
Reviewers: Kirigami, hein
Reviewed By: hein
Subscribers: plasma-devel
Tags: Kirigami
Differential Revision: https://phabricator.kde.org/D7939