Load QtQuick settings

Summary:
Loads settings on whether QtQuick uses GL or software rendering

Aurorae needed a fix. The rest "just works" with up-to-date plasma framework.

Test Plan:
Alt tabbed
Showed an OSD
Grepped kwin's QML for any custom shaders.
(which is the only part that doesn't work here)

Reviewers: #plasma, graesslin

Reviewed By: #plasma, graesslin

Subscribers: graesslin, plasma-devel, kwin, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D8040