Add KCM for adjusting QtQuick Rendering in Plasma
Summary:
Does what you imagine it would.
It's akin to KWin's compositor settings, designed to be hidden away and
not used by 99%.
Test Plan:
Set some values
Looked at config.
Unset set values
Reviewers: Plasma, mart
Reviewed By: Plasma, mart
Subscribers: abetts, mart, graesslin, alexeymin, sebas, broulik, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D7934