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.