Set desktop entry name for the Qt GUI

This will make the GUI program show the correct icon in the desktop
environment.

src/bubblejail/bubblejail_gui_qt.py

@@ -669,6 +669,7 @@ def __init__(self, parent: BubblejailConfigApp):
 class BubblejailConfigApp:
     def __init__(self) -> None:
         self.q_app = QApplication(argv)
+        self.q_app.setDesktopFileName("bubblejail-config")
         self.window = QMainWindow()
         self.window.resize(600, 400)
         self.switch_to_selector()