Add MergingTransformer and SplittingTransformer
MergingTransformer: runtime number of the same input type -> one output, SplittingTransformer: N compile time known inputs -> runtime number of same type outputs As migration path, implement ListTransformer in terms of MergingTransformer.
Finally, add some syntactic sugar to compose Traits to FunctionalUtilities, and a function which can update the 'key' of a DataObjectHandle Property
add syntactic sugar to FunctionalUtilities