Removed ZooKeeper API usage, renamed packages

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