Updating currencies, adding minor units

Hello! This MR updates the currencies (ISO 4127) in line with the latest standard. It also adds the "minor_units" field which is included in the standard, which shows the number of digits after the decimal separator (i.e. the ratio between the currency and its minor unit, as a power of 10). It was mentioned here you'd be happy to add that field. I've checked the data using the validate_json_data.py script, if anything needs changing let me know. Thanks.