PR for #2604.

• New operation: liquidity_pool_update_operation
  • operation_type = 75
  • default fee 1 BTS

   struct liquidity_pool_update_operation : public base_operation
   {
      asset                    fee;                ///< Operation fee
      account_id_type          account;            ///< The account who owns the liquidity pool
      liquidity_pool_id_type   pool;               ///< ID of the liquidity pool
      optional<uint16_t>       taker_fee_percent;       ///< Taker fee percent
      optional<uint16_t>       withdrawal_fee_percent;  ///< Withdrawal fee percent
      extensions_type extensions;  ///< Unused. Reserved for future use.
   };
  

Note:

• The withdrawal fee percentage of a liquidity pool can be updated by the owner, but only to zero.
• The taker fee percentage of a liquidity pool can be updated at any time by the owner if the withdrawal fee percentage is zero.