PlaneReflector Support for Side-by-Side Rendering

- The PlaneReflector class now supports side-by-side rendering.  This
does mean that while in this rendering style that all planar reflections
are rendered twice, as reflection is a screen space effect from the eye
point of view.
- Planar reflections now work in the Oculus Rift.
- Modified GuiTSCtrl::onRender() to move up where the rendering style is
defined to just before the reflection manager has its turn.
Merge pull request #505 from DavidWyand-GG/PlanarReflectionFix

PlaneReflector Support for Side-by-Side Rendering