moved several files around

Mostly moved classes that became node derivatives into the node/ folder.

app/node/audio/pan/pan.h

@@ -31,6 +31,8 @@ class PanNode : public Node
 public:
   PanNode();
 
+  NODE_DEFAULT_DESTRUCTOR(PanNode)
+
   virtual Node* copy() const override;
 
   virtual QString Name() const override;

app/node/audio/volume/volume.h

@@ -31,6 +31,8 @@ class VolumeNode : public MathNodeBase
 public:
   VolumeNode();
 
+  NODE_DEFAULT_DESTRUCTOR(VolumeNode)
+
   virtual Node* copy() const override;
 
   virtual QString Name() const override;