Fix MainWindow parenting

Author: ferdnyc

src/classes/app.py

@@ -242,7 +242,7 @@ def __init__(self, *args, mode=None):
 
         # Create main window
         from windows.main_window import MainWindow
-        self.window = MainWindow(mode)
+        self.window = MainWindow(self, mode=mode)
 
         # Reset undo/redo history
         self.updates.reset()