Add formatting for EUR locales

[zachgoll]

This PR sets up some basic "exceptions" for formatting currencies.

As of now, we format currencies in the UI based on the following logic:

1. We maintain a list of currencies with default formatting metadata in currencies.yml
2. The Money and Money::Currency classes read this list and provide a method, format_options
3. We have a global helper, format_currency which uses Rails number_to_currency(format_options) to format the currency

This works in 95% of cases, but there are some cases where a single currency like EUR should be formatted differently based on the locale of the user.

#1226 enabled setting locales for each user. We are now able to pass the configured locale directly to the format_options method on the Money class to "override" the default formatting.

For example, 25123.98 in the EUR currency will be formatted as follows based on the user's locale:

• €25,123.98 - for en
• €25.123,98 - for de

This PR will certainly not cover all exceptional cases, but sets up an easy way to add these via locale_options:

def locale_options(locale)
  case [ currency.iso_code, locale.to_sym ]
  when [ "EUR", :nl ], [ "EUR", :pt ]
    { delimiter: ".", separator: ",", format: "%u %n" }
  when [ "EUR", :en ], [ "EUR", :en_IE ]
    { delimiter: ",", separator: "." }
  else
    {}
  end
end

[zachgoll]

legacy, not being used anywhere