data: saving typedef to Storage

This change save typedef expressions to the Storage using a node of type Node::NODE_TYPEDEF and an edge of type
Edge::EDGE_TYPEDEF_OF that leads to the original type, with the qualifiers saved as DataType on the edge.

src/lib/data/graph/Edge.cpp

@@ -103,6 +103,8 @@ std::string Edge::getTypeString() const
 		return "is derived from";
 	case EDGE_CALL:
 		return "calls";
+	case EDGE_TYPEDEF_OF:
+		return "is typedef of";
 	default:
 		LOG_ERROR("TypeString not implemented for edge type.");
 	}