[timeline] split refreshand setting of data

fixtracks/widgets/detectiontimeline.py

@@ -157,12 +157,18 @@ class DetectionTimeline(QWidget):
         # self.setMaximumHeight(100)
         # self.setSizePolicy(QSizePolicy.Policy.Expanding, QSizePolicy.Policy.Fixed)
 
-    def setData(self, data:TrackingData):
-        logging.debug("Timeline: setData!")
-        self._data = data
+    def clear(self):
         for i in self._scene.items():
             if isinstance(i, (QGraphicsLineItem, QGraphicsEllipseItem)):
                 self._scene.removeItem(i)
+
+    def setData(self, data:TrackingData):
+        logging.debug("Timeline: setData!")
+        self._data = data
+        self.update()
+
+    def update(self):
+        self.clear()
         self.draw_coverage()
 
     def draw_coverage(self):