Summary:
Removes a tonne of complex code, means any future improvements to our
QtQuick integration only need to be in one place.

QML logic remains in Aurorae as it does complex things. All other
aurorae specialties remain.

Only functional difference is that we now use a shared GL context
between window frames, which Plasma::FrameSVG will make use of.

Test Plan:
kcmshell5 kwindecoration
ran some aurorrae themes on my kwin. Look the same as master

Reviewers: #kwin, mart

Reviewed By: mart

Subscribers: mart, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D25206