Gedit 47.0 compatibility

[yochananmarqos]

The plugin no longer works as of 47.0.

Traceback (most recent call last):
  File "/home/yochanan/.local/share/gedit/plugins/ex-mortis/__init__.py", line 330, in on_app_window_added
    self.setup_window(window)
  File "/home/yochanan/.local/share/gedit/plugins/ex-mortis/__init__.py", line 224, in setup_window
    window_manager.track_window(window)
  File "/home/yochanan/.local/share/gedit/plugins/ex-mortis/windowmanager.py", line 103, in track_window
    connect_handlers(
  File "/home/yochanan/.local/share/gedit/plugins/ex-mortis/utils/__init__.py", line 61, in connect_handlers
    handler_ids.append(target.connect(signal, fn, *args))
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^