XD-722 Batch - Add notification channel support

- Adds a notification (output) channel to the channel registry

The following steps should illustrate the added behavior

    xd> job create --name myjobname --definition "job"
    xd> stream create --name jobnotifications --definition ":myjobname > log"
    xd> stream create --name webinput --definition "http > :myjobname"

Jira: https://jira.springsource.org/browse/XD-722