statistics: convert HistogramMarkers to QSGNodes

This is in analogy to the quartile markers.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

stats/histogrammarker.h

@@ -0,0 +1,21 @@
+// A line to show median an mean in histograms
+#ifndef HISTOGRAM_MARKER_H
+#define HISTOGRAM_MARKER_H
+
+#include "chartitem.h"
+
+class StatsAxis;
+class StatsView;
+
+// A line marking median or mean in histograms
+class HistogramMarker : public ChartLineItem {
+public:
+	HistogramMarker(StatsView &view, double val, bool horizontal, QColor color, StatsAxis *xAxis, StatsAxis *yAxis);
+	void updatePosition();
+private:
+	StatsAxis *xAxis, *yAxis;
+	double val;
+	bool horizontal;
+};
+
+#endif