jvpp: adding callbacks for all messages (VPP-914)

1) In the previous version callbacks were generated based on
request-replay naming conventions. It turned out they were too
strict in case of events (e.g. BFD sends Details messages as
notifications). So now we generate callback for all messages,
allowing to receive any message as notification.(callback_gen.py)
2) "notification" suffix is no longer added because all messages
are treated same (dto_gen.py, jvpp_c_gen_.py)
3) name of property that holds notification/events changed in callback
facade and future apis
4) JVppNotification.java is no longer used since all events are treated
equally

Change-Id: I13f6438affc3473040d63cd4acb3984d03e97482
Signed-off-by: Matej <matej.perina@pantheon.tech>