Qt GL 2 paint engine doesn't work with GL 3.2 core profile

We need to change the GL engine to not use client side vertex / index arrays, as these are not supported any more. They need to be replaced by buffer objects all the way through.

Also, glGetString(GL_EXTENSIONS) is no longer supported and glGetStringi() must be used instead. See attached patch for initial attempt to get the paint engine working with GL 3.2 Core.