Add new Maven module to manage NBI Notifications

Add new Maven module to manage NBI Notifications

- Implement a new Maven module named nbinotifications containing classes
  capable of communicating with Kafka server
- Add the class Subscriber capable of reading events from topics Kafka
- Add the class Publisher capable of writing events from topics Kafka
- Add yang file nbi-notifications to model the service notifications
- Implement a new RPC API named GetNotificationsService capable of
  returning the notifications stored in a topic Kafka
- Implement a new RPC API named publishNotificationService in charge of
  publishing a message in Kafka topic
- Add a listener to the RPC GetNotificationsService
- Add new blueprint in nbinotifications
- Add unit tests to check the functionning of nbinotifications classes
- Update pom.xml to implement the new module nbinotifications

JIRA: TRNSPRTPCE-343
Signed-off-by: Thierry Jiao <thierry.jiao@orange.com>
Change-Id: I74298292034e4a158b27dd5db47e63918026684b