Implementing MySQL Logging support...

Logging to MySQL via TCP or UNIX socket.

Additional configuration field introduced: "common" (containing generic configuration items).
"sensorid" configuration item introduced - it is used by MySQL logging so that multiple sensors logging to a single MySQL server can be distinguished.

WARNING:

This features relies on the python package MySQL-python which itself depends on libmysqlclient-dev. The MySQL-python dependency was added to requirements.txt, libmysqlclient-dev was added to travis.yml, but it might be missing on existing deployments.