implement "type" for xml node data

app/widget/nodeview/nodeview.cpp

@@ -45,6 +45,7 @@ const double NodeView::kMinimumScale = 0.1;
 
 NodeView::NodeView(QWidget *parent) :
   HandMovableView(parent),
+  NodeCopyPasteService(QStringLiteral("nodes")),
   drop_edge_(nullptr),
   create_edge_(nullptr),
   create_edge_output_item_(nullptr),

app/widget/timelinewidget/timelinewidget.cpp

@@ -60,6 +60,7 @@ namespace olive {
 
 TimelineWidget::TimelineWidget(QWidget *parent) :
   super(true, true, parent),
+  NodeCopyPasteService(QStringLiteral("timeline")),
   rubberband_(QRubberBand::Rectangle, this),
   active_tool_(nullptr),
   use_audio_time_units_(false),