added save functions to various classes

Each class is responsible for its own saving and loading from the XML data
in order to reduce the complexity of the save code.

app/node/input.h

@@ -54,6 +54,8 @@ public:
 
   virtual QString name() override;
 
+  virtual void Save(QXmlStreamWriter* writer) const override;
+
   /**
    * @brief The data type this parameter outputs
    *
@@ -238,6 +240,9 @@ signals:
 
   void KeyframeRemoved(NodeKeyframePtr key);
 
+protected:
+  virtual void SaveInternal(QXmlStreamWriter* writer) const;
+
 private:
   /**
    * @brief Returns whether a data type can be interpolated or not