Feature/kafka guide app

Initial commit of Kafka Ingestion Guide. This is specifically for Kafka Cluster version 0.8.x.
the \`Kafka08ConsumerFlowlet`, which is designed to work with a 0.8.x Kakfa Cluster. If you want to use the application with a 0.7.x Kakfa Cluster, please refer to \[cdap-kafka-pack](https://github.com/caskdata/cdap-packs) for information 
on how to build a 0.7.x Kafka Subscriber Flowlet.