Refactor: Promote opcodes to protocol_binary.h

Keep all protocol opcodes in a single place. Drop
the deprecated opcodes from 1.7..

Change-Id: I0ac521fc8fd86aa5488f09f21255796ef9464523
Reviewed-on: http://review.couchbase.org/37113
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>