Remove glew dependencies that cause Qt conflicts

Remove the glew dependencies that cause conflicts with Qt. Qt5 should provide the necessary functions for OpenGL. See:

• https://stackoverflow.com/questions/28235640/using-latest-opengl-functions-across-classes-in-qt-5-4
• https://doc.qt.io/qt-5/qopenglfunctions-4-5-core.html

This means that support for Qt4 needs to be dropped.

Requirement for some new functionality, e.g. VR.