Resolve "[Sirius] Asset diagram doesn't present contained Asset anymore"

Add support for 2 areas in an Asset to show the attributes and the contained Asset (using vertical stack)

Add support for both "containment" boxes:

• Asset contained in an Asset
• Asset defined in a sub group

The box priority is given to Asset in an Asset, in that case, if the contained Asset isn't defined in the same group/subgroup as its container Asset, then its label is longer and shows the full qualified name.

Adapted direct edit of the label to take into account only the name.

• Dragging an Asset from any place to an Asset, will update or create the containment link, but it will not change the AssetGroup/subGroup of the Asset.
• Dragging an Asset to the diagram background or to an AssetGroup will change the asset group. Note: due to the presentation priority, if the Asset is also contained by an asset then only the label will change
• A popup action is available to remove an Asset from its Asset container (the action is filtered to show up only on contained Assets)

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• Closes #348 (closed)
• Closes #347 (closed)
• Contribues #340 (closed)