Port DesktopGrid QtQuickWindow to EffectQuickView
Lots of red, does the same thing in a simplified way avoiding creating a
real window and having to hack round it.
Test Plan: Click add and remove, remove button disables appropriately
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: meven, zzag, kwin
Differential Revision: https://phabricator.kde.org/D26381