Make GLES implementations happy.

Change-Id: Ib389e379f23794eee0fa71ca26b863e56cee662e
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>

[ChangeLog] Added QOpenGLWindow. This serves as a convenience class for
creating windows showing OpenGL content via an API similar to QGLWidget
and without any widget dependencies.

Done-with: Jorgen Lind <jorgen.lind@digia.com>
Task-number: QTBUG-36899
Change-Id: I52e9bc61acb129dbfd3841b3adeffab2dbcf7f05
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>