reflections - demo update (v15)

Just one thing added for this update but it's fairly big:

Planar reflections

• These are more accurate reflections for windows, mirrors and glass doors.
• Can be turned on or off at "Options/Graphics/Planar reflections".
• There is also a "min. size" setting that determines the minimum on-screen size of the surface for the reflections to be visible.
• Those who enable planar reflections can reduce the "Env. map resolution" setting to substantially reduce video memory usage with minimal visual impact.