make block values input parameters rather than class members

This allows these values (length and media in) to be modified in the node
graph and for all the automated node input functions to work with them.

app/node/block/block.h

@@ -55,7 +55,7 @@ public:
   void set_in(const rational& in);
   void set_out(const rational& out);
 
-  const rational& length() const;
+  rational length() const;
   virtual void set_length(const rational &length);
   virtual void set_length_and_media_in(const rational &length);
 
@@ -64,7 +64,7 @@ public:
   void set_previous(Block* previous);
   void set_next(Block* next);
 
-  const rational& media_in() const;
+  rational media_in() const;
   void set_media_in(const rational& media_in);
 
   const QString& block_name() const;
@@ -102,8 +102,8 @@ protected:
   Block* next_;
 
 private:
-  rational length_;
-  rational media_in_;
+  NodeInput* length_input_;
+  NodeInput* media_in_input_;
 
   rational in_point_;
   rational out_point_;
@@ -112,6 +112,9 @@ private:
 
   QVector<Block*> linked_clips_;
 
+private slots:
+  void LengthInputChanged();
+
 };
 
 #endif // BLOCK_H