- Added backend for NATS message broker
- removed unneeded test script

- monitoring/test_monitoring.py: provides a basic testing skeleton
- monitoring/requirements.in/.txt: updated with pytest
- monitoring/genproto.py: added instructions to import generated Python modules using "from . import ..." instead of "import ..."; otherwise, pytest and other possible modules doing imports might complain.
- monitoring/monitoring_server.py: packed start_server and stop_server functionaity to simplify test definition, minor formattings, bug resolutions and improvements in package import.
- monitoring/monitoring_client.py: minor formattings, bug resolutions, and improvements in package import.