Move non-instance application members to static fields

Signed-off-by: Pavel Artsishevsky <polter.rnd@gmail.com>

bbswitch_gui/application.py

@@ -29,6 +29,10 @@
 class Application(Gtk.Application):
     """Main application class allowing only one running instance."""
 
+    bbswitch = BBswitchMonitor()
+    client = BBswitchClient()
+    nvidia = NvidiaMonitor(timeout=REFRESH_TIMEOUT)
+
     def __init__(self, *args, **kwargs) -> None:
         """Initialize application instance, setup command line handler."""
         super().__init__(
@@ -62,10 +66,6 @@ def __init__(self, *args, **kwargs) -> None:
         self.window: Optional[MainWindow] = None
         self.indicator: Optional[Indicator] = None
 
-        self.bbswitch = BBswitchMonitor()
-        self.client = BBswitchClient()
-        self.nvidia = NvidiaMonitor(timeout=REFRESH_TIMEOUT)
-
     def update_bbswitch(self) -> None:
         """Update GPU state from `bbswitch` module."""
         logging.debug('Got update from bbswitch')