What's new:
- docker support (#142)
- allow property value to be a sys env var in main.properties (part of #206)
- upgrade data type of db column "connector_meter_value.value" to TEXT (#212)
- make registration status of BootNotification configurable (#202)
- improve conformity to spec about AuthorizationStatus ConcurrentTx (#219)
- bug fixes: #215
- update dependencies