Bug 33216: Catch and handle RegisterRequired exceptions for SIP fee paid messages

Bug 33216: Catch and handle RegisterRequired exceptions for SIP fee paid messages

If registers are being used in Koha, they are required. If a SIP account has no register and a fee paid message is sent, the SIP server crashes and the client never gets a response. It would be much better if Koha would response with 38 response where "payment accepted" is N, and an AF field stating that the SIP account needs to be associated with a register.

Test Plan:
1) Enable UseCashRegisters, set RequireCashRegister to "always require a
   cash register". Do *not* set a cash register for the SIP account you
   will be testing with.
2) Using the SIP cli tester, send a fee paid message for a patron owing
   fees.
3) Note the lack of a SIP response
4) Apply this patch
5) Restart the SIP server
6) Repeat step 2, you should now get a SIP response with the error
   message in it!

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>