Add const values for BatchHeader.ServiceClassCode and BatchControl.ServiceClassCode

[bkmoovio]

We have a fair amount of hard-coded values, which aren't that friendly for developers. If we provide names it should help to understand them.

Example: BatchHeader.ServiceClassCode: 200, 220, 225, 280

Identifies the general classification of dollar entries to be exchanged (i.e. debit and/or credit entries)
–200 ACH Entries Mixed Debits and Credits
–220 ACH Credits Only
–225 ACH Debits Only
–280 ACH Automated Accounting Advice

Create developer friendly meaningful constants for these values and modify the code to reference the constants.