BUG-614: convert NotificationBrokerImpl

This does a straight xtend->java conversion by moving xtend-generated
java files into the repository instead of xtend. This is the first step
in optimizing NotificationBrokerImpl.

Change-Id: Ie8dc1dfb6c5b9e80a8d79a5de31410100b35c7fc
Signed-off-by: Robert Varga <rovarga@cisco.com>