Bring all funtions in database_api and wallet_api to a unified form

Some functions have different api.

For example:

fc::optional<son_object> get_son_by_account(account_id_type account) const;

fc::optional<witness_object> get_witness_by_account(const std::string account_id_or_name) const;

Some funtions doesn't have implementation in wallet_api or in database_api.

Need to bring them all to unified form.