Reorganise renderer settings

[Floppy]

We currently have 4 render modes, one of which includes shadows, but ideally that should be separate. We should have different surface material modes:

• Original (including textures, default)
• Fixed (default material only)
• Direction (surface coloured by normal vector)

Then extra rendering features can be enabled on any of them:

• Lighting styles
• Shadowing
• Stereo

Even better, this should be swappable live in the renderer, rather than as a user setting (though maybe we keep the settings for a default?)