Pretty-printing as utility methods

These two commits aim to better support evaluation of user input data.

- `CountryCodes.SHORTEST_IBAN_LENGTH` and `CountryCodes.LONGEST_IBAN_LENGTH` can be used to find the right dimension for input fields
- `IBAN.toPretty()` reformats user-input without validation to assist user in finding typos (especially if user entered IBAN without spaces)
- Removed country-code-pre-check in `IBAN`-constructor as `CountryCodes.getLengthForCountryCode()` already rejects he filtered values and some more
- Reduced length check in `IBAN`-constructor to a minimum of 5 as `CountryCodes.getLengthForCountryCode()` may some day return 14 and this way only one place needy to be changed; 4 could be argued as well, but I guess there will never be a country with just one bank account...
- Switched from `String.replaceAll()` to pre-compiled pattern (same semantics, possibly faster)