Today DataItemSet got a lot simpler 
It no longer keeps track of an internallist but instead
provides a AsEventedList<T>() method which you can use to get an adapted 'list' version of the set.
This works by returning an adapter which implement IEventedList<T> but redericts all calls to a list
of dataitems. Changes in the dataitems are propagated as changes in the list and ideally the model-developer only uses the list.
Breaking changes:
- No longer can use Value as a hook to get the internallist ...there is no internal list.