Add support for configuring Kafka Producers

You may now build a managed and configured Kafka `Producer` in the same way as
you can build managed and configured Kafka Consumers.

Also adds support for `snappy` compression to both consumer and
producer.
Fixes to KafkaConsumerFactory.

Fixes incorrect names on some setter methods and adds the
`@JsonProperty` annotation to the recovery options.
Fix CuratorHealthCheck failing with namespace

When Curator has been initialized with a namespace, the
`CuratorHealthCheck` would always fail.
Remove unnecessary imports
Add dropwizard-extra-kafka7 module

Provides a consumer-only implementation for the older 0.7 release of
Apache Kafka.
Make Kafka Producer's Managed

Producer's should be properly managed by the Dropwizard lifecycle.

Also fixes incorrect capitalization in the producer package name.
Fix Curator namespace config never being valid

Curator expects namespaces to omit the leading `/`, whereas ZooKeeper
expects the leading `/`. This causes `CuratorFactory` to always fail to
build an instance.

Let's be defensive and strip any leading `/` from the configured
ZooKeeper namespace when initializing the Curator instance.

Fixes #25.
Bump to 0.7.1-2-SNAPSHOT for local release while waiting on upstream release