Added more SEC transaction types and updated documentation

Haven't heard of the 9s populating the empty lines after the File Control record.

I've made the CRM id of the customer in the payment an optional field since it is optional according to the NACHA standard.

Length of lines are now dependent on `$this->recordsize` instead of hardcoded value `94`. Enables expansion in case record size needs to be manually set and changed in the future.

`NachaFile::setSettlementAccount()` is never used in generating the NACHA. Flagged as inactive.