Get Parent of Referable

[FrankSchnicke]

As suggested in #29, getting the parent of a Referable would be useful.

[arnoweiss]

Not exactly sure how this could work - mostly because I don't know what Parent means. For example, I don't think that a AAS is the Parent of a Submodel since Submodels aren't included in AASs but referred to from an AAS. Either way, such a function would always require the full Environment to know where to search.

public Referable getParent(Referable referable, Environment env)

Additionally (and perhaps out of scope here) - I think I'd be particularly useful to get the Submodel for a SME. That's something different since an SMEs parent could always be a SMEC, SMEL, Entity or AnnotatedRelationshipElement. So the signature would could like this:

public Identifiable getIdentifiableRoot(Referable referable, Environment env)