adds the possibility to use on_message_ext which gets the whole MosaicMessage passed as an argument
CARE: To test this, you have to implement a service which implements the on_message_ext function. The "image_adder.py" test service worked as an example and can be used.
CARE: To test this, you have to implement a service which implements the on_message_ext function. The "image_adder.py" test service worked as an example and can be used.