Allow template parameter substitution's actual to reference the source binding template parameters.
Currently it is not possible to successfully select a template parameter as the 'actual' of a template parameter substitution from the 'Select type' list, as doing so results in the error
Selected element (?) is not an instance of a UMLClassifier.
However it is possible to create a reference to a template parameter by entering the parameter name in the actual's input field and selecting the desired parameter from the suggestion list. However this become very cumbersome.
A reference is important because it allows changes to the actual's reference to propagate automatically e.g. renaming the source template parameter.