move item setting to a node flag

app/node/project/folder/folder.cpp

@@ -34,6 +34,8 @@ const QString Folder::kChildInput = QStringLiteral("child_in");
 
 Folder::Folder()
 {
+  SetFlag(kIsItem);
+
   AddInput(kChildInput, NodeValue::kNone, InputFlags(kInputFlagArray | kInputFlagNotKeyframable));
 }
 

app/node/project/folder/folder.h

@@ -86,11 +86,6 @@ public:
     return item_children_;
   }
 
-  virtual bool IsItem() const override
-  {
-    return true;
-  }
-
   int index_of_child(Node* item) const
   {
     return item_children_.indexOf(item);