Fix #767: NPE for IBAN with country code

[manosbatsis]

Fixes #767

There is no easy way to control target country randomization when creating IBANs, because both countryCodeToBasicBankAccountNumberPattern and createCountryCodeToBasicBankAccountNumberPatternMap() are private.

This PR adds a Finance.ibanCountryCodes() to allow finer control of scope.

[bodiam]

Hi @manosbatsis , thanks for submitting this fix. I'd suggest trying out Datafaker, a drop in replacement for Javafaker. We're also very open to contributions!

[manosbatsis]

Hey @bodiam, actually I think datafaker's Finance class has the same issue. Perhaps you'd like the same PR there?

[bodiam]

Can you reproduce it with Datafaker? If so, absolutely!