dropped remains of old-style vbucket update tracking

Change-Id: I3ccb6bc492ac91e1a586f2c7a6ed9c54c7a863c6
Reviewed-on: http://review.couchbase.org/40087
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
introduced xdcr_sup

Change-Id: I6cdc497375729a181e4b176bded547dd64ed9e3c
Reviewed-on: http://review.couchbase.org/40088
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
moved xdc_replication state definition out of .hrl and into .erl

Change-Id: If928d4a23f2e9c7487cace733c74326d546ad37f
Reviewed-on: http://review.couchbase.org/40089
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
avoid xdc_rep_manager call for xdcr stats/errors gathering

Because we can do it directly without any extra serialization implied
by gen_server:call.

Change-Id: Ib9b0f0feb9d49320cf6c665fe680ce839d79282c
Reviewed-on: http://review.couchbase.org/40090
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>