Bug 570056 - Comment and ret value automatically added when saving class diagram

- Adapt to designer changes in the context of Bug 570056
- Add a comment about the deviation from the designer superclass

Change-Id: Ida1e91f2e072e456ff0992d23b288fe30b3cb7f5
Signed-off-by: Ansgar Radermacher <ansgar.radermacher@cea.fr>