Fix modify_order and misc improvements

In this release,

• Fix by @Jianqoq for parsing of modify orders.
• Fix by @Jianqoq for requesting historical schedule with use_rth flag.
• Add subscribe_daily_pnl by @Jianqoq to properly retrieve the account-level PNL.
• Add test or modify_order and add replace_order.
• Add request_managed_accounts for multi-accounts.