The graphics header node is a replacement for the timeline when the Gantt chart control is being used in a multi Gantt chart context, for example when used in a DualGanttChartContainer or a MultiGanttChartContainer.
This node can be set by calling GanttChart.setGraphicsHeader(Node). The node passed to this method can be anything. The only important thing to be aware of is that the preferred height of this node has to be set to the same value as the preferred height of the tree table header.
