public interface FactoryHelper<T>
Helper to identify the exact nature of a Shape being dragged from the Palette into a Canvas. The purpose of this is to
allow a single ShapeFactory to create multiple (but similar) different Shapes. For example you might have a ShapeFactory
that creates "Letters of the Alphabet". It is a single factory and it's "Shape" is a single letter. You could add multiple
PaletteShapes to the Palette, one for each letter of the alphabet, and use FactoryHelper to specify which letter has been selected.