PPMN_ — Inconsistent and redundant model for DerivedFrom

Unlike other relationships this has subclasses for the different types of derivation. But also a DerivationKind (though indirectly linked via DerivationType) with largely the same Library of instances (DerivedFrom, QuotedFrom, RevisionOf, SourcedFrom), though missing subclass DescendantOf (which is self-referentially defined).

BTW there's a missing word "one" in the following under Figure 24
"DerivationTypes support the definition of the expected kinds of derivations that might result in the generation of one EntityType from or more others."

Remove DerivedFrom subclasses and add DescendantOf DerivationKind

The inconsistency will be removed by removing the subclasses of DerivedFrom, adding an association from DerivedFrom to DerivationKind (similar to other typed elements), and adding DescendantOf as a DerivationKind to the library.