Fix TODO: MessageDispatcher: Remove per-id signal when there is no more subscribers.
Fix TODO: MessageDispatcher: Remove per-id signal when there is no more subscribers.

Change-Id: I8ff7c8bea1de46ae657a04388a28e409a57578cd
Reviewed-on: http://gerrit.aldebaran.lan:8080/8132
Reviewed-by: cgestes <ddb78fe00abb42f91254c16a0860e38eb0781789@aldebaran-robotics.com>
Tested-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>

aldebaran/libqi,aldebaran/libqi-java,vbarbaresi/libqi,aldebaran/libqi,aldebaran/libqi-java,aldebaran/libqi-java,bsautron/libqi,aldebaran/libqi