remove old image capability from DasAnnotation object #144
Description
The original DasAnnotation object would allow either a granny text string or an image to be placed on the canvas. If the URL property was set, then the GrannyTextRenderer would be null and the image would be drawn at a scale determined by the scale property. Images should be implemented now as an extension in the Granny Text, where the GrannyTextRenderer can insert an image in-line.
This odd second-mode code should be deprecated and removed. The old property can remain, but then be implemented as the GTR extension.