Add a shutdown signal

Provide a way for code that is not a modRana module to cleanup on shutdown
without the need for modules to trigger the cleanup on shutdown.

It is now enough to just connect to the shutdown_signal provided by the modrana singleton. :)

modrana.py

@@ -128,7 +128,9 @@ def __init__(self):
             'name': ""
         }
 
+        # signals
         self.notificationTriggered = Signal()
+        self.shutdown_signal = Signal()
 
         self.mapRotationAngle = 0 # in radians
         self.notMovingSpeed = 1 # in m/s
@@ -515,6 +517,8 @@ def shutdown(self):
         log.info("Shutting-down modules")
         for m in self.m.values():
             m.shutdown()
+        # trigger the shudown signal
+        self.shutdown_signal()
         self._saveOptions()
         modrana_log.log_manager.disable_log_file()
         log.info("Shutdown complete (%s)" % utils.get_elapsed_time_string(start_timestamp))