added clone functions for nodes

Since nodes are are extremely derivative types, we use a clone/copy function
to produce new types of the derived class easily.

app/node/node.h

@@ -50,6 +50,14 @@ class Node : public QObject
 public:
   Node();
 
+  /**
+   * @brief Creates a clone of the Node
+   *
+   * By default, the clone will NOT have the values and connections of the original node. The caller is responsible for
+   * copying that data with functions like CopyInputs() as copies may be done for different reasons.
+   */
+  virtual Node* copy() = 0;
+
   /**
    * @brief Return the name of the node
    *