corrected the association between Relationship and InterfaceProvidingRequiringEntity to be bidirectional (with InterfaceProvidingRequiringEntity being the container)

git-svn-id: https://se1.informatik.uni-wuerzburg.de/usvn/svn/code/DMM/trunk@16338 9e42b895-fcda-4063-8a3b-11be15eb1bbd