Ecore object diagram does not show dangling object correctly

[hallvard]

The ecore object diagram support shows the sub-tree rooted at the selection. If some object in this sub-tree references an object outside this tree, it is shown as a class with name null (source: o4 -- "affiliation" onull). The null should be the instance nr., but since this object isn't shown, it has no number.

[hallvard]

The fix just adds the dangling object. Could perhaps show in a separate color, but it will be apparent it's dangling, since it will not be contained in any object.