node: merge various metadata functions into one

app/node/project/folder/folder.cpp

@@ -37,9 +37,13 @@ Folder::Folder()
   AddInput(kChildInput, NodeValue::kNone, InputFlags(kInputFlagArray | kInputFlagNotKeyframable));
 }
 
-QIcon Folder::icon() const
+QVariant Folder::data(const DataType &d) const
 {
-  return icon::Folder;
+  if (d == ICON) {
+    return icon::Folder;
+  }
+
+  return super::data(d);
 }
 
 void Folder::Retranslate()

app/node/project/folder/folder.h

@@ -59,7 +59,7 @@ public:
     return tr("Organize several items into a single collection.");
   }
 
-  virtual QIcon icon() const override;
+  virtual QVariant data(const DataType &d) const override;
 
   virtual void Retranslate() override;