Position markers correctly and update with scroll

app/widget/timeruler/seekablewidget.h

@@ -60,6 +60,10 @@ public slots:
 
   void UpdateMarkers();
 
+  void addMarker(TimelineMarker* marker);
+
+  void updateMarkerPositions();
+
 protected:
   void SeekToScreenPoint(int screen);
 
@@ -111,6 +115,8 @@ private:
 
   QVector<Marker*> marker_widgets;
 
+  QMap<TimelineMarker*, Marker*> marker_map_;
+
 };
 
 }