Remove setup_viewport method and enter/exit.

The viewport shouldn't dictate how the scene
is rendered. It also simplies the OpenGL state
management if this code is managed by the client
application and not PyGLy.
Add setup_render_parameters method to examples.

This performs the task of the recently removed
viewport.setup_viewport.
Legacy examples add glShadeMode with GL_SMOOTH
and enable GL_RESCALE_NORMALS.