[TIMOB-2401] iOS: Several localization enhancements

See #1870 for the initial, Android implementation directives from our customer.

Add to Ti.Locale:

getCurrentLanguage() - returns language string such as "en".

getCurrentCountry() - returns "US" for example.

getCurrentLocale() - returns "en-US" for example.

getCurrencyCode(locale_string) - e.g., pass "en-US" and it will return "USD"

getCurrencySymbol(currency_code) - e.g., pass "USD" and it will return "$"

getLocaleCurrencySymbol(locale_string) - e.g., pass "en-US" and it will return "$"

Locale and format string support for String.formatDecimal:

String.formatDecimal(2.5) - returns 2.5 formatted in current locale. If a european locale, for example, will return "2,5".

String.formatDecimal(2.5, "000.000") - e.g., returns "002.500" if current locale is en_US, or "002,500" if current locale is de_AT.

String.formatDecimal(2.5, 'de-AT') - returns "2,5"

String.formatDecimal(2.5, 'de-AT', '000.0000') - returns "002,50000"

You can exercise these with this simple program (app.js):

/*global Ti, Titanium, alert, JSON */
Titanium.UI.setBackgroundColor('#000');
var win = Titanium.UI.createWindow({  
    title:'Test',
    backgroundColor:'#fff',
    fullscreen: true,
    exitOnClose: true
});

var rows = [];
function makeRow(title) {
    rows.push(Ti.UI.createTableViewRow({title: title}));
}

var statements = 
    ['Ti.Locale.getCurrentLanguage()',
     'Ti.Locale.getCurrentCountry()',
     'Ti.Locale.getCurrentLocale()',
     'Ti.Locale.getCurrencyCode(Ti.Locale.getCurrentLocale())',
     'Ti.Locale.getCurrencyCode("en-GB")',
     'Ti.Locale.getCurrencyCode("-GB")',
     'Ti.Locale.getCurrencySymbol("EUR")',
     'Ti.Locale.getCurrencySymbol("GBP")',
     'Ti.Locale.getLocaleCurrencySymbol("en-US")',
     'String.formatDecimal(2.5)',
     'String.formatDecimal(2.5, "000.00")',
     'String.formatDecimal(2.5, "de-DE")',
     'String.formatDecimal(2.5, "de-DE", "000.00")'
     ];
                  
for (var i = 0; i < statements.length; i++) {
    makeRow(statements[i] + " = " + eval(statements[i]));
}

win.add(Ti.UI.createTableView({data:rows}));

win.open();