Removed ZooKeeper Native API usage

The prototype no longer uses the ZooKeeper API directly.
All ZooKeeper access is done via Curator. Since Curator
also includes APIs for embeeded ZooKeeper servers,
our home grown embedded ZooKeeper classes were also
removed.
Refactored package names

xdzk.cluster
Classes for working with cluster members, in particular with
Containers.

xdzk.curator
Utilities for Curator.

xdzk.server
Server classes, including Admin and Container.