deprecate some models and models fields:

-- events concept
-- all optional fields

Change-Id: I473576e4fd3998b4bceeebc1d9b3169f517ba364
Reviewed-on: http://review.couchbase.org/31068
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>