REST API for CxnDefs

Currently, the ARIS Repository API handles connections between objects only indirectly. To retrieve them, the query API has to be used, which does not return the information in the same consistent way that objects and models use. Creating CxnDefs is possible only indirectly by creating a dummy model and create MODELCONNECTIONs there.

Direct, consistent API calls for CxnDefs creation, retrieval und deletion would be desirable.