Push notifications follow-up

 * Exposing an HTTP server on the `OAE.tenantServer` object
 * Moved `sockjs` logic into oae-activity/lib/rest
 * Consolidated naming of routes and streams.
        ```
        streamType = 'activity' | 'notification' | 'message'
        activityStreamId = resourceId + '#' + streamType
        ```
      Everything should now be using the terminology:
        * resourceId (c:cam:abc123)
        * activityStreamType (notification)
        * activityStreamId (c:cam:abc123#notification)
 * Renamed some registry methods
     registerActivityStream --> registerActivityStreamType
 * Cleaned up JSDocs and unit test names
 * The ActivityAPI now emits structured data in the form of
     {
        'u:cam:abc123#activity': {
             'resourceId': 'u:cam:abc123',
             'streamType': 'activity',
             'activity': <Activity>
        }
     }