Fix issue with pages copied with ctrl + dnd

Ctrl + drag & drop creates referenced pages. Operations (e.g. rotate)
done to a referenced page will be applied to all pages it reference to.
That is not what we want. All pages should be "real" copies.
Fix pdfarranger#410

pdfarranger/pdfarranger.py

@@ -1181,11 +1181,12 @@ def iv_dnd_received_data(self, iconview, context, _x, _y,
                              for p in data]
             iter_to = self.model.get_iter(ref_to.get_path())
             for ref_from in ref_from_list:
-                row = model[model.get_iter(ref_from.get_path())]
+                iterator = model.get_iter(ref_from.get_path())
+                page = model.get_value(iterator, 0).duplicate()
                 if before:
-                    it = model.insert_before(iter_to, row[:])
+                    it = model.insert_before(iter_to, [page, page.description()])
                 else:
-                    it = model.insert_after(iter_to, row[:])
+                    it = model.insert_after(iter_to, [page, page.description()])
                 path = model.get_path(it)
                 iconview.select_path(path)
             if move: