move navigation to new file

src/main/jastadd/Navigation.jrag

+aspect Navigation {
+  inh PetriNet PnObject.petriNet();
+  eq PetriNet.getChild().petriNet() = this;
+
+  coll java.util.Set<PnObject> PetriNet.allObjects() [new java.util.HashSet()] root PetriNet;
+  PnObject contributes this
+    to PetriNet.allObjects()
+    for petriNet();
+
+  coll java.util.Set<Place> PetriNet.allPlaces() [new java.util.HashSet()] root PetriNet;
+  Place contributes this
+    to PetriNet.allPlaces()
+    for petriNet();
+}

src/main/jastadd/References.jrag

@@ -9,14 +9,6 @@ aspect References {
     throw new RuntimeException(new de.tudresden.inf.st.pnml.PnmlParseException("Unable to resolve id " + id));
   }
 
-  coll java.util.Set<PnObject> PetriNet.allObjects() [new java.util.HashSet()] root PetriNet;
-  PnObject contributes this
-    to PetriNet.allObjects()
-    for petriNet();
-
-  inh PetriNet PnObject.petriNet();
-  eq PetriNet.getChild().petriNet() = this;
-
   eq PnObject.globallyResolveArcByToken(String id) = (Arc) petriNet().resolve(id);
   eq PnObject.globallyResolveNodeByToken(String id) = (Node) petriNet().resolve(id);
   eq PnObject.globallyResolvePlaceNodeByToken(String id) = (PlaceNode) petriNet().resolve(id);