Feature request: Image/SVG overlay

[YasharF]

In some cases, it would be helpful to have an image or vector drawing with some opacity render on the X-Y plane, at the lowest z data point, or at some offset. An example would be to add an outline of the US States in the Demo Vote example. Another example would be to load a custom logo or watermark. Another example would be to load a data point of interest with a different symbol.

I suspect loading such an image would require some parameters for offset and scaling.

A stretch goal for this feature is to import a 3D model for 3D plots.