implemented footage loading from projects

Footage is a special case where the node parameters can reference objects that
exist outside of the graph. Therefore specific code is needed to
serialize/deserialize.

app/project/item/folder/folder.h

@@ -21,6 +21,8 @@
 #ifndef FOLDER_H
 #define FOLDER_H
 
+#include "node/param.h"
+#include "project/item/footage/footage.h"
 #include "project/item/item.h"
 
 /**
@@ -40,7 +42,7 @@ public:
 
   virtual QIcon icon() override;
 
-  virtual void Load(QXmlStreamReader* reader) override;
+  virtual void Load(QXmlStreamReader* reader, QHash<quintptr, StreamPtr> &footage_ptrs, QList<NodeParam::FootageConnection> &footage_connections) override;
 
   virtual void Save(QXmlStreamWriter* writer) const override;