-added imagery for 2004 and 2005
-explicitly set zIndex option for all tileLayers so that the imagery and base layers load properly relative to one another
-changed sequence to add overlayMaps layers using list with keys and called next load function upon complete of last ajax get operation so that they load in the correct order every time
-changed show/hide of operational layers to show()/hide() layer functions instead of setting opacity to 0, should improve performance
-moved loading display to bottom of screen
-added errorTileUrl to imagery layers in attempt to stop console get tile error, but no success