Initialize Gst before use speech

In sugar gst was initialized at startup, now we need initialize Gst
in the speech code.

src/sugar3/speech.py

@@ -227,6 +227,7 @@ class _GstSpeechPlayer(GObject.GObject):
     }
 
     def __init__(self):
+        Gst.init(None)
         GObject.GObject.__init__(self)
         self._pipeline = None
         self._all_voices = None