Don't start key rotation listener until we connect to socket

We're seeing evidence of post-export Chrome apps causing problems with
the Standalone install that imported the data. They both try to rotate
signed prekeys.

js/background.js

@@ -93,7 +93,6 @@
         }
 
         Whisper.WallClockListener.init(Whisper.events);
-        Whisper.RotateSignedPreKeyListener.init(Whisper.events);
         Whisper.ExpiringMessagesListener.init(Whisper.events);
     });
 
@@ -119,6 +118,8 @@
 
         if (messageReceiver) { messageReceiver.close(); }
 
+        Whisper.RotateSignedPreKeyListener.init(Whisper.events);
+
         var USERNAME = storage.get('number_id');
         var PASSWORD = storage.get('password');
         var mySignalingKey = storage.get('signaling_key');