+ Add structure
+ Rename KAFKA_BOOTSTRAP_SERVERS_DEFAULT to KAFKA_BOOTSTRAP_DEFAULT

+ consistency for property oder
+ spellings

`KafkaRecordSender` does not only support sending Avro values in combination
with the Confluent Schema Registry anymore, but also arbitrary other
types using a custom serializer.

new output: AggregatedPowerRecords
refactoring: remove inferable types
set id in combine function of aggregator