Give created QGraphicsScenes a parent

Ensure the scene is deleted at the same time as the widget.
Fix an runtime error at process exit when running tests with PyQt 5.14

Orange/widgets/unsupervised/owhierarchicalclustering.py

@@ -266,7 +266,7 @@ def on_annotation_changed(value):
 
         gui.auto_send(box, self, "autocommit", box=False)
 
-        self.scene = QGraphicsScene()
+        self.scene = QGraphicsScene(self)
         self.view = StickyGraphicsView(
             self.scene,
             horizontalScrollBarPolicy=Qt.ScrollBarAlwaysOff,

Orange/widgets/visualize/owboxplot.py

@@ -263,7 +263,7 @@ def __init__(self):
             stateWhenDisabled=False)
 
         gui.vBox(self.mainArea, addSpace=True)
-        self.box_scene = QGraphicsScene()
+        self.box_scene = QGraphicsScene(self)
         self.box_scene.selectionChanged.connect(self.commit)
         self.box_view = QGraphicsView(self.box_scene)
         self.box_view.setRenderHints(QPainter.Antialiasing |

Orange/widgets/visualize/owmosaic.py

@@ -324,7 +324,7 @@ def __init__(self):
 
         self.areas = []
 
-        self.canvas = QGraphicsScene()
+        self.canvas = QGraphicsScene(self)
         self.canvas_view = ViewWithPress(
             self.canvas, handler=self.clear_selection)
         self.mainArea.layout().addWidget(self.canvas_view)

Orange/widgets/visualize/owsieve.py

@@ -121,7 +121,7 @@ def __init__(self):
             self.attr_box, self, "Score Combinations", self.set_attr)
         self.vizrank_button.setSizePolicy(*fixed_size)
 
-        self.canvas = QGraphicsScene()
+        self.canvas = QGraphicsScene(self)
         self.canvasView = ViewWithPress(
             self.canvas, self.mainArea, handler=self.reset_selection)
         self.mainArea.layout().addWidget(self.canvasView)

Orange/widgets/visualize/owsilhouetteplot.py

@@ -179,7 +179,7 @@ def __init__(self):
         # Ensure that the controlArea is not narrower than buttonsArea
         self.controlArea.layout().addWidget(self.buttonsArea)
 
-        self.scene = QGraphicsScene()
+        self.scene = QGraphicsScene(self)
         self.view = StickyGraphicsView(self.scene)
         self.view.setRenderHint(QPainter.Antialiasing, True)
         self.view.setAlignment(Qt.AlignTop | Qt.AlignLeft)

Orange/widgets/visualize/owvenndiagram.py

@@ -100,7 +100,7 @@ def __init__(self):
         self.area_keys = []
 
         # Main area view
-        self.scene = QGraphicsScene()
+        self.scene = QGraphicsScene(self)
         self.view = QGraphicsView(self.scene)
         self.view.setRenderHint(QPainter.Antialiasing)
         self.view.setBackgroundRole(QPalette.Window)