Move KGLDisplay constructor, assignment operator and destructor to protected members, as they should be for singletons.
Move KGLDisplay constructor, assignment operator and destructor to protected members, as they should be for singletons.

KDE/gluon,cgaebel/gluon,pranavrc/example-gluon,pranavrc/example-gluon,KDE/gluon,pranavrc/example-gluon,cgaebel/gluon,KDE/gluon,KDE/gluon,cgaebel/gluon,pranavrc/example-gluon,cgaebel/gluon