Adding icons and graph management

modeling/AVATAR/testDependencyGraphs.xml

src/main/java/ui/graphd/GraphDEdgeConnector.java

src/main/java/ui/graphd/GraphDPanel.java

src/main/java/ui/graphd/GraphDVertex.java

src/main/java/ui/util/IconManager.java

src/main/resources/ui/util/graphvertex.gif