Introduce "derived" annotation, i.e. based on calculations instead of explicit annotations / model contents can be implemented

- DerivedAnnotationBase meta-model element, with getValue() EOperation, and a extensive documentation.
- Corresponding DerivedAnnotationValueProviderBase, implementing a read-only, text-view of the calculation result
- To implement the above, move handling of annotation EClass & factory to ValueProviderBase

refs 1841