Add dropwizard-curator and dropwizard-zookeeper

Extracts ZooKeeper functionality from `dropwizard-core` to a new module,
`dropwizard-zookeeper`.

    * Adds new `namespace` option to `ZooKeeperConfiguration` to sandbox
    an application to a particular namespace in ZooKeeper.
    * Replaces `ZooKeeperHealthCheck` and `ZooKeeperQuorumHealthCheck`
    with a single `ZooKeeperHealthCheck` that ensures the configured
    namespace exists in the ensemble.

Also adds a new module `dropwizard-curator` for integrating with the
`Curator` library by Netflix.
Add validation for ZooKeeper namespace

Provides a utility class for representing ZooKeeper ZNode paths which
validates the Path.

Namespaces specified in the `ZooKeeperConfiguration` are now required to
be valid.
Round out ZooKeeper support.
Fix parameter indentation
Clean up HealthCheck names

Also improve `ZooKeeperHealthCheck` to detect partial failures.
Extract `RetryPolicy` from `CuratorConfiguration`
Improve support for ZooKeeper and Curator
Merge branch 'develop' into feature/zookeeper-curator

Conflicts:
	dropwizard-extra-hbase/src/main/java/com/datasift/dropwizard/hbase/config/HBaseClientConfiguration.java
	dropwizard-extra-zookeeper/src/main/java/com/datasift/dropwizard/zookeeper/config/ZooKeeperConfiguration.java
Clean up some docs
Fix imports
Improve ZNode#equals
Add zookeeper exclusion for log4j/slf4j

These conflict with the logging from Dropwizard, so we should exclude
them.
Add read-only support to ZooKeeper

Now supports read-only quorums.

Includes minor refactoring of namespace configuration validation and
improved tests for ZooKeeperConfiguration.
Integrate Curator with dw-extra-zookeeper

All `ZooKeeper` instances that Curator creates are now created via the
`ZooKeeperFactory` included in `dropwizard-extra-zookeeper`. This allows
Curator to automatically benefit from improvements to
`ZooKeeperFactory`.
Add test resources for ZooKeeper module

ZooKeeperConfigurationTest was missing its test configuration file.
Add Curator configuration test
Merge branch 'develop' into feature/zookeeper-curator

Conflicts:
	dropwizard-extra-zookeeper/pom.xml
Round out Curator/ZooKeeper integration

Adds configuration options to Curator for:

    * Exponential back-off (replaces customisable retryPolicy)
    * Compression codec

Adds configuration options to ZooKeeper for:

    * Authorization details
Add compression to curator test config
Update versions to 0.6.2-1-SNAPSHOT