various node UI improvements

app/node/graph.h

@@ -27,14 +27,21 @@
 
 class NodeGraph : public QObject
 {
+  Q_OBJECT
 public:
   NodeGraph();
 
+  void AddNode(Node* node);
+
   const QString& name();
   void set_name(const QString& name);
 
   QList<Node*> nodes();
 
+signals:
+  void EdgeAdded(NodeEdgePtr edge);
+  void EdgeRemoved(NodeEdgePtr edge);
+
 private:
   QString name_;
 };