began node viewer for dag insight

app/node/graph.cpp

@@ -20,6 +20,8 @@
 
 #include "graph.h"
 
+#include "qobjectlistcast.h"
+
 NodeGraph::NodeGraph()
 {
 
@@ -34,3 +36,8 @@ void NodeGraph::set_name(const QString &name)
 {
   name_ = name;
 }
+
+QList<Node *> NodeGraph::nodes()
+{
+  return static_qobjectlist_cast<Node>(children());
+}