Preferences, singletons

Create a Preference dialog for fonts and audio output devices

Turn Preferences and SoundOff into singletons.  No matter how many times
you request a new one, the same instance is returned.

Stop using singals on the parent() to access other instances, such as
sound and Preferences.

lib/sounds.py

@@ -11,6 +11,13 @@ from PyQt6.QtMultimedia import (
 
 
 class SoundOff(QObject):
+    _instance = None
+    def __new__(cls):
+        if cls._instance:
+            return cls._instance
+        cls._instance = super(SoundOff, cls).__new__(cls)
+        return cls._instance
+    
     def __init__(self):
         super().__init__()
         #
@@ -95,7 +102,6 @@ class SoundOff(QObject):
             self.localPlayer.play()
         if not self.virtualDevice:
             return
-        return
         self.virtualPlayer.setSource(src)
         self.virtualPlayer.setPosition(0)
         if not self.virtualPlayer.audioOutput():