Add the ability to return the Item pixel value when identifying image services

At the moment the item pixel value of image services cannot be returned when identifying an image service in the HTML5 viewer. The item pixel value is part of the image service architecture. It is a value from a catalog item. In the pop-up in ArcGIS Online it is configured as {Raster.ItemPixelValue}.

Example: the item pixle of the following image service should show the height abouve sea level in meters: https://ahn.arcgisonline.nl/arcgis/rest/services/Hoogtebestand/AHN3_r/ImageServer

Currently there is no way to configure this in Geocortex Essentials, even if identify operations are turned on and catalog items are included. When requesting the same service in ArcGIS Online the pixel value shows as expected. 

The following video shows the behaviour in GVH and in ArcGIS Online: http://somup.com/crVi6qonkV. The value that is shown in the map tip in GVH is not the height but a different value, presumably a cell value or somthing like this.

It would be great if the item pixel value could be returned by default or by using a certain configuration in Geocortex Essentials.