Bug fix / moved z-index and animation properties

Solved an issue where the preload animation wasn't actually animating.

The base z-index of the script's zoom/loading animation can now be
controlled by setting the "elevation" property of the FancyZoom
singleton (the default value is 500, as per the original script). The
width, height, frame count and URI of the loading animation can all be
adjusted too, if need be.