Stream module graceful undeployment/destroy

When a stream is undeployed (by marking the 'deployed' flag to
'false' in the stream data in ZK) the admin listener will
remove the source, processors, and sink paths in the order
in which the stream is processed.

Furthermore, when a stream is destroyed via the REST controller,
the stream will be undeployed before it is deleted from ZK.
See StreamDeployer.beforeDelete() for details.