Add 'stats vbucket-seqno' command

This command lists all of the high sequence numbers for all
vbuckets.

Change-Id: Ie007d9549857a2b485d7df43931be23a04b2c23c
Reviewed-on: http://review.couchbase.org/30778
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>
MB-9484: Move all functions out of TapProducer class

Change-Id: I1332619f132b2980962e21d6eb43984f7a4bbb51
MB-9484: Move most of Producer logic into TapProducer

A lot of the logic in the Producer class will not be used
by the UprProducer. This change moves that logic back into
the TapProducer class.

Change-Id: If04715468340e848d857e8641407eaa75e6035aa
MB-9484: Allow upr to schedule backfills and send mutations/deleted

Change-Id: I1c8edf8f809626a56ff648c83799253c81a5410a