let performance specification inherit from identifier

tools.descartes.dni.core/META-INF/MANIFEST.MF

tools.descartes.dni.core/model/DNIMM3.xcore

...s.dni.core/src/tools/descartes/dni/dnimm3/DNIPackage.java

.../tools/descartes/dni/dnimm3/PerformanceSpecification.java

...e/src/tools/descartes/dni/dnimm3/impl/DNIPackageImpl.java

...c/tools/descartes/dni/dnimm3/impl/EndPerformanceImpl.java

...escartes/dni/dnimm3/impl/IntermediatePerformanceImpl.java

.../tools/descartes/dni/dnimm3/impl/PerformanceLinkImpl.java

...rtes/dni/dnimm3/impl/PerformanceNetworkInterfaceImpl.java

...ols/descartes/dni/dnimm3/impl/PerformanceSdnNodeImpl.java

...artes/dni/dnimm3/provider/EndPerformanceItemProvider.java

.../dnimm3/provider/IntermediatePerformanceItemProvider.java

...rtes/dni/dnimm3/provider/PerformanceLinkItemProvider.java

...mm3/provider/PerformanceNetworkInterfaceItemProvider.java

...s/dni/dnimm3/provider/PerformanceSdnNodeItemProvider.java

...i.core/src/tools/descartes/dni/dnimm3/util/DNISwitch.java