TEIIDDES-1048 ModelExtensionAssistant API Should Be Changed To Remove Methods That Pertain To Namespaces Other Than Their Own. Lots of refactoring to assistants and rest of framework. Now assistants are only responsible for/knowledgeable of their model extension definition and their properties. Assistants now know nothing of a registry. Created an aggregator object that knows how to accumulate information from all assistants.