Generate simple consumer and/or producer with an entity (via Kafka module)

[fdelbrayelle]

Steps:

1. Generate a JHipster project with the main generator and the Kafka option.
2. Install and launch the Kafka module.
3. Kafka module asks a first question: "Do you want to generate a consumer, a producer or both?" (multi-choices)
4. Kafka module asks a second question: "For which entities?" (multi-choices)
5. Kafka sub generator generates the consumer, the producer or both. The only format for the moment is JSON (we could add Avro and String in the future if needed). The generator creates also a GenericConsumer and a GenericProducer. The tests "*ConsumerIT" and "*ProducerIT" will be also generated.