Integrating Kafka partitioning scheme with Voldemort cluster.xml

- Rename KafkaConsumerDefinition to KafkaTopicDefinition as it will be used by both client and server
- Read from cluster.xml to initialize the VeniceStore
- Add consistent partition, serializing classes for Kafka to use
- Adding KafkaRoutedStore object for producing objects into Kafka
Maybe add the special byte (always 0 for now) at this level? I'm not sure where is the best place.