MB-8013 Detailed rebalance progress UI.

Change-Id: I224a16a47d84a0661626509158aa7f59da90c3d5
Reviewed-on: http://review.couchbase.org/25910
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>