BUG-2288: DOMNotification API

This API definition tries to fix the missing pieces in the
CompositeNode-centered APIs, such as inability to drop a notification
rather than waiting for resources needed to publish it to become
available.

Also adds missing documentation to the DOMService concept, which is used
by the two services being defined.

Change-Id: I93d22cf6121a7cf231b2da424e94d14b59fb883f
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-2288: DOMNotification API"