Move command opcodes to memcached

And rename them all to PROTOCOL_BINARY_

Change-Id: I674cfb8dcf5817d76a973cfda8ef86df32815f51
Reviewed-on: http://review.couchbase.org/37115
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>