To minimize OpenGL/Qt issues, we now set the default surface format
before QApplication is instantiated.

Further, pqQVTKWidget explicitly requests stereo-capable surface-format
when crystal-eyes stereo was requested using command line options for
each pqQVTKWidget instance separately, if possible. On platforms without
support for quad-buffer (e.g. macOS), it will generate a warning that
the stereo request is being ignored.