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/inputdragger.h

@@ -21,7 +21,9 @@
 #ifndef NODEINPUTDRAGGER_H
 #define NODEINPUTDRAGGER_H
 
-#include "node/input.h"
+#include "common/rational.h"
+#include "node/keyframe.h"
+#include "node/param.h"
 
 namespace olive {
 
@@ -32,21 +34,17 @@ public:
 
   bool IsStarted() const;
 
-  void Start(NodeInput* input, const rational& time, int track, int element = -1);
+  void Start(const NodeKeyframeTrackReference& input, const rational& time);
 
   void Drag(QVariant value);
 
   void End();
 
 private:
-  NodeInput* input_;
-
-  int track_;
+  NodeKeyframeTrackReference input_;
 
   rational time_;
 
-  int element_;
-
   QVariant start_value_;
 
   QVariant end_value_;