Implement credit deal auto-repayment feature

PR for #2595.

Changes:

Add enum class credit_deal_auto_repayment_type

/// Defines automatic repayment types
enum class credit_deal_auto_repayment_type
{  
  /// Do not repay automatically
  no_auto_repayment = 0,
  /// Automatically repay fully when and only when the account balance is sufficient
  only_full_repayment = 1,
  /// Automatically repay as much as possible using available account balance
  allow_partial_repayment = 2,
  /// Total number of available automatic repayment types
  CDAR_TYPE_COUNT = 3
};

Update type of extensions field of credit_offer_accept_operation struct, add an auto_repay field inside, so that accounts can decide whether and how to automatically repay when accepting a credit offer

struct credit_offer_accept_operation : public base_operation
{  
  struct ext
  {  
     /// After the core-2595 hard fork, the account can specify whether and how to automatically repay
     fc::optional<uint8_t> auto_repay;
  };
  asset                    fee;                ///< Operation fee
  account_id_type          borrower;           ///< The account who accepts the offer
  credit_offer_id_type     offer_id;           ///< ID of the credit offer
  asset                    borrow_amount;      ///< The amount to borrow
  asset                    collateral;         ///< The collateral
  uint32_t                 max_fee_rate = 0;   ///< The maximum acceptable fee rate
  uint32_t                 min_duration_seconds = 0; ///< The minimum acceptable duration
  extension<ext> extensions; ///< Extensions
};

New operation: credit_deal_update_operation, so that credit deal owners can change whether or how to automatically repay

operation_type = 76

default fee 1 BTS

struct credit_deal_update_operation : public base_operation
{
struct fee_params_t { uint64_t fee = 1 * GRAPHENE_BLOCKCHAIN_PRECISION; };

asset                    fee;                ///< Operation fee
account_id_type          account;            ///< The account who owns the credit deal
credit_deal_id_type      deal_id;            ///< ID of the credit deal
uint8_t                  auto_repay;         ///< The specified automatic repayment type
extensions_type extensions;  ///< Unused. Reserved for future use.
};

Rename all fee_parameters_type in the codebase to fee_params_t to get around the "string table overflow" issue in MinGW build

bitshares / bitshares-core

Implement credit deal auto-repayment feature #2735