function setDefaultLocale(locale) {
        if (isValidLocaleDefinition(locale)) {
            return formatDefaultLocale(locale);
        } else {
            throw new Error(WRONG_LOCALE_OBJECT_MESSAGE);
        }
    }
Sets the given locale as the new default locale through d3-format's formatDefaultLocale
When an object is used, it simply uses it to set the new locale.
@param  {LocaleObject} locale    The desired locale object
@return {Object}                 Object with a 'format' and 'formatPrefix' functions