use strings to connect nodes

This makes the node system somewhat more high-level with the intent of making
working with them far more flexible and stable. By making the architecture more
abstracted, it becomes far less rigid which should allow us to do even more
with it and make it much less crash prone.

app/node/inputimmediate.h

@@ -53,7 +53,12 @@ public:
     return standard_value_;
   }
 
-  void set_standard_value_on_track(const QVariant &value, int track = 0);
+  const QVariant& get_split_standard_value_on_track(int track) const
+  {
+    return standard_value_.at(track);
+  }
+
+  void set_standard_value_on_track(const QVariant &value, int track);
 
   void set_split_standard_value(const SplitValue& value);