MB-11707: disambiguate xdcr incoming ops/sec stat

We display that single stat in two places. So in order to disambiguate
it w.r.t. large graph title we provide bigTitle attribute for stat
description.

Change-Id: I227f6dfb0ece1a2aa68f13b4ddb5a1520ef9544f
Reviewed-on: http://review.couchbase.org/39361
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>