ShapeDescriptos should convert images to BinaryProcessor

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CUrrently the shape descriptors accept several kinds of images yet they really work only on binary images.

It should be checked if the application should be restricted to a ByteProcessor or BinaryProcessor

• http://rsbweb.nih.gov/ij/developer/api/ij/process/BinaryProcessor.html
• http://rsbweb.nih.gov/ij/developer/api/ij/process/ByteProcessor.html