DerivedAnnotationBase -> IDerivedAnnotation<T>

 - Change return type of getValue() to T
 - This allows for more type safe implementation of the underlying calculations
 - The former abstract base class DerivedAnnotationBase used Object as a return type for getValue() to due an EMF code generation bug for generics if the base class is located in a different .ecore file than the concrete class. For interfaces, this bug is not triggered.
  
refs 1841