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.

ui/MainWindow.ui

@@ -80,7 +80,7 @@
      <x>0</x>
      <y>0</y>
      <width>800</width>
-     <height>32</height>
+     <height>24</height>
     </rect>
    </property>
    <widget class="QMenu" name="menuFile">
@@ -109,6 +109,7 @@
     </widget>
     <addaction name="menuBooks_2"/>
     <addaction name="menuPeople"/>
+    <addaction name="actionPreferences"/>
    </widget>
    <addaction name="menuFile"/>
    <addaction name="menuBooks"/>
@@ -159,6 +160,11 @@
     <string>Read Book</string>
    </property>
   </action>
+  <action name="actionPreferences">
+   <property name="text">
+    <string>Preferences</string>
+   </property>
+  </action>
  </widget>
  <resources/>
  <connections>