429439: [Class diagram] Link Contaiment graphical representation
https://bugs.eclipse.org/bugs/show_bug.cgi?id=429439

-Replace default implementation of NodePlate by Ellipse
-Use Ellipse form implementation from common found in component

Signed-off-by: Mickael ADAM <Mickael.ADAM@ALL4TEC.net>
Merge branch 'bugs/429439' of https://github.com/Gabitchov/org.eclipse.papyrus.git into bugs/429439