Extend get_block_header API and get_block_header_batch API to optionally return witness signatures

Follow-up of #2641, for issue #2588.

Instead of always returning witness signatures (as in #2641), this PR adds an optional with_witness_signature parameter to the get_block_header API, and add an optional with_witness_signatures parameter to the get_block_header_batch API, to indicate whether to return witness signatures.

This PR also updates the return types of these 2 APIs so that witness signature can optionally be returned. The new type maybe_signed_block_header is derived from block_header with an optional witness_signature field.

   struct maybe_signed_block_header : block_header
   {
      optional<signature_type> witness_signature;
   };

Updated APIs:

get_block_header( block_num, with_witness_signature )

  /** 
   * @brief Retrieve a block header
   * @param block_num Height of the block whose header should be returned
   * @param with_witness_signature Whether to return witness signature. Optional.
   *                               If omitted or is @a false, will not return witness signature.
   * @return header of the referenced block, or null if no matching block was found
   */
  optional<maybe_signed_block_header> get_block_header(
        uint32_t block_num,
        const optional<bool>& with_witness_signature = optional<bool>() )const;

get_block_header_batch( block_nums, with_witness_signatures )

  /** 
   * @brief Retrieve multiple block headers by block numbers
   * @param block_nums vector containing heights of the blocks whose headers should be returned
   * @param with_witness_signatures Whether to return witness signatures. Optional.
   *                                If omitted or is @a false, will not return witness signatures.
   * @return array of headers of the referenced blocks, or null if no matching block was found
   */
  map<uint32_t, optional<maybe_signed_block_header>> get_block_header_batch(
        const vector<uint32_t>& block_nums,
        const optional<bool>& with_witness_signatures = optional<bool>() )const;

bitshares / bitshares-core

Extend get_block_header API and get_block_header_batch API to optionally return witness signatures #2652