moved several files around

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

app/node/math/math/mathbase.h

@@ -30,6 +30,8 @@ class MathNodeBase : public Node
 public:
   MathNodeBase() = default;
 
+  NODE_DEFAULT_DESTRUCTOR(MathNodeBase)
+
   enum Operation {
     kOpAdd,
     kOpSubtract,