[CNT-144] OSS General Prepare Contract Type Support #132

The new smart contract architecture has two input addresses in function call transaction, so we need oss to support it.

OSS 這支 API 支援 op_return 且 type 為 contract
base/v1/general-transaction/prepare

交易範例
TX_ID

user_addr  amount(color) -> p2sh_addr1 amount(color)

                            p2sh_addr2 amount(color)

                            op_return amount(color)