add mode for copying values only and not connections

Sometimes we'll be copying nodes without wanting to copy their connections,
since we'll want to connect them to equivalent copies rather than connecting
them to the same nodes the originals were connected to. We now have an extra
parameter to distinguish such operations.

app/node/input.h

@@ -131,7 +131,7 @@ public:
   /**
    * @brief Copy all values including keyframe information and connections from another NodeInput
    */
-  static void CopyValues(NodeInput* source, NodeInput* dest);
+  static void CopyValues(NodeInput* source, NodeInput* dest, bool include_connections = true);
 
 signals:
   void ValueChanged(const rational& start, const rational& end);