renamed some classes, moved pathChildrenCache initialization/start code
to a separate ZooKeeperConfigurationSource.start() method.  added
ZooKeeperConfigurationSource.close() method to support the Closeable
interface.

reduced the visibility of WatchedUpdateResult's constructors to
package-private to encourage the use of the Factory method.
adjusted test to favor the ZK property override over the System property
per archaius 0.5.3+.  see https://github.com/Netflix/archaius/issues/62
for more info.