Add containment Reference (or container) in ABS with dedicated sirius representation

We need a way to nest box in the sirius representations

a simplified version would be to add a boolean "container" on AssetReference

( a better version would require to deal with opposite (container/containment) and use it )

• add container attribute in ASBS.ecore
• add sirius odesign support to use the container and represent it as nested boxes
• add checker to verify that we do not have more than one container reference set on a given Asset