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/block/block.h

@@ -114,21 +114,6 @@ public:
 
   virtual void Retranslate() override;
 
-  NodeInput* length_input() const
-  {
-    return length_input_;
-  }
-
-  NodeInput* media_in_input() const
-  {
-    return media_in_input_;
-  }
-
-  NodeInput* speed_input() const
-  {
-    return speed_input_;
-  }
-
   TransitionBlock* in_transition()
   {
     return in_transition_;
@@ -166,6 +151,11 @@ public:
 
   virtual void Hash(QCryptographicHash &hash, const rational &time) const override;
 
+  static const QString kLengthInput;
+  static const QString kMediaInInput;
+  static const QString kEnabledInput;
+  static const QString kSpeedInput;
+
 public slots:
 
 signals:
@@ -178,7 +168,7 @@ protected:
 
   rational MediaToSequenceTime(const rational& media_time) const;
 
-  virtual QVector<NodeInput*> GetInputsToHash() const override;
+  virtual void InputValueChangedEvent(const QString& input, int element) override;
 
   virtual void LinkChangeEvent() override;
 
@@ -188,11 +178,6 @@ protected:
 private:
   void set_length_internal(const rational &length);
 
-  NodeInput* length_input_;
-  NodeInput* media_in_input_;
-  NodeInput* speed_input_;
-  NodeInput* enabled_input_;
-
   rational in_point_;
   rational out_point_;
   Track* track_;