Add QtOpenGLWindowBase as base class and implement QtOpenGLWindow to render using a Painter
Fix errors in cmake files
Implement SimpleTexture-example as a Painter in its own library, making it independent from the used windowing library
ViewerQt: Use example library to instanciate a painter, remove direct example
Create standard event handler for gloperate-glfw equal to QtOpenGLWindow. Move globjects initialization into the windowing backend rather than a painter