ContainerServer constructor fixes

Introduced new Paths class to hold path constants. This can
serve as a replacement for the more sophisticated Path
enum since Curator has the ability to ensure full
path creation.

Introduced use of Curator namespace feature to automatically
prefix all paths with /xd.

Moved initialization of PathChildrenCache from ContainerServer
constructor to onConnect. During testing I noticed that
a cache cannot be reopened when closed, so a new instance
is created when a connection is established.

Moved StreamWriter to the tests area since it has a dependency
on a test class.
AdminServer implementation with Curator
Fixes from https://github.com/markfisher/xdzk/pull/8
Introduced Container domain classes

Added some simple Container domain classes and supporting
interfaces. The ContainerAware interface provides access to
an iterator over all Containers in the cluster. ChildPathIterator
is a generic iterator over children nodes in a Curator/ZooKeeper
path.
Bug fixes

When a SUSPENDED event is raised we cancel the leader selector
and the containers childre cache. If a LOST event is the next
event we attempt another close which results in IllegalStateException.
This exception can be ignored since these objects were no longer
in a usable state.

Fixed an NPE in ContainerListener.

Logged leader interruption at level INFO.
Added copyright headers