Use build_data instead of serializer for obelisk

This requires regular hashes to be in the right order, so it cannot be committed until libbitcoin/libbitcoin#144 is merged.

This commit causes libbitcoin-client to handle its own weird byte-reversals internally, so it no longer relies on the libbitcoin serializer to handle that. With this in place, libbitcoin itself can then correct its own serializer.