Added support for <duration>float</duration> to the slideshow3D .xml format

to allow the time for autostepping between layers/slides.

Moved the tiles accross to the left hands side by default.

examples/slideshow3D/SlideEventHandler.h

@@ -58,6 +58,8 @@ public:
     void setTimeDelayBetweenSlides(double dt) { _timePerSlide = dt; }
     double getTimeDelayBetweenSlides() const { return _timePerSlide; }
     
+    double getCurrentTimeDelayBetweenSlides() const;
+
 protected:
 
     ~SlideEventHandler() {}