Improved new_window handling.

Remove new_window hook.
Plugin informed of all windows via events when first loaded.
init_qt no longer needed for exchange_rate plugin.

plugins/audio_modem.py

@@ -35,10 +35,6 @@ class Plugin(BasePlugin):
                 'Linux': 'libportaudio.so'
             }[platform.system()]
 
-    @hook
-    def init_qt(self, gui):
-        pass
-
     def is_available(self):
         return amodem is not None