Change order of GUI signalling and trigger disabling to avoid multiple button presses (related to #16)

photobooth/Photobooth.py

@@ -215,8 +215,8 @@ class Photobooth:
 
         logging.info('Photobooth triggered')
 
-        self._conn.send(GuiState.GreeterState())
         self.triggerOff()
+        self._conn.send(GuiState.GreeterState())
 
         self.setCameraActive()
         self.recvAck()