Merge branch 'develop' into feat/monitoring-subscriptions

# Conflicts:
#	src/common/DeviceTypes.py
#	src/context/service/grpc_server/ContextServiceServicerImpl.py
#	src/device/service/drivers/__init__.py
#	src/policy/src/main/java/eu/teraflow/policy/PolicyServiceImpl.java
#	src/policy/src/main/java/eu/teraflow/policy/model/PolicyRuleBasic.java
#	src/policy/src/main/java/eu/teraflow/policy/monitoring/MonitoringGateway.java
#	src/policy/src/main/java/eu/teraflow/policy/monitoring/MonitoringService.java
#	src/policy/src/test/java/eu/teraflow/policy/SerializerTest.java
#	src/service/service/path_computation_element/PathComputationElement.py
#	src/webui/service/static/topology_icons/Acknowledgements.txt