moved several files around

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

app/node/math/math/math.h

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