Much refactoring

This seems to work, needs more testing

sound_objects/intern/speaker_utils.py

@@ -0,0 +1,18 @@
+def all_speakers(scene):
+    return [obj for obj in scene.objects if obj.type == 'SPEAKER']
+
+
+def solo_speakers(scene, solo_group):
+    for speaker in all_speakers(scene):
+        if speaker in solo_group:
+            speaker.data.muted = False
+        else:
+            speaker.data.muted = True
+
+        speaker.data.update_tag()
+
+
+def unmute_all_speakers(scene):
+    for speaker in all_speakers(scene):
+        speaker.data.muted = False
+        speaker.data.update_tag()