Core: restore "CompositeValue" wording (#339).

The "ChildTopics" wording is revoked.

de.deepamehta.core.CompositeValue               # Interface (represents an attached Object)
de.deepamehta.core.model.CompositeValueModel    # Model class (CompositeValue in DM 4.0.14)

DeepaMehtaObject:
    - CompositeValue getCompositeValue()

DeepaMehtaObjectModel:
    - CompositeValueModel getCompositeValueModel()

CompositeValue:
    - CompositeValueModel getModel()

See ticket 339.