Refactored pkg/netmap package provides JSON converters for
NodeInfo and PlacementPolicy structures, that has been used
by client applications.
It also updates Node structure itself so it is a part of
grpc <-> v2 <-> pkg conversion chain.
Signed-off-by: Alex Vanin <alexey@nspcc.ru>
Netmap source interface used by object service to build
placement based on current or previous network map.
Signed-off-by: Alex Vanin <alexey@nspcc.ru>
