code: use macros for default node functions

Easier to maintain

app/node/generator/polygon/polygon.cpp

@@ -61,11 +61,6 @@ PolygonGenerator::PolygonGenerator()
   poly_gizmo_ = new PathGizmo(this);
 }
 
-Node *PolygonGenerator::copy() const
-{
-  return new PolygonGenerator();
-}
-
 QString PolygonGenerator::Name() const
 {
   return tr("Polygon");

app/node/generator/polygon/polygon.h

@@ -39,9 +39,7 @@ class PolygonGenerator : public GeneratorWithMerge
 public:
   PolygonGenerator();
 
-  NODE_DEFAULT_DESTRUCTOR(PolygonGenerator)
-
-  virtual Node* copy() const override;
+  NODE_DEFAULT_FUNCTIONS(PolygonGenerator)
 
   virtual QString Name() const override;
   virtual QString id() const override;