for `en` language use GB formatting in DatePicker

• date format in DatePicker is changed from American style MM/dd/yyyy to European dd/MM/yyyy

• first day of week is changed from Sunday to Monday This follow latest changes in formatByPattern, what switch default en locale from en-US to en-GB

  In case someone need American-style, the following can be added for en language in customer model locale/lang-en.json

{
  "el": {
    "datepicker": {
      "format": {
        "date": "MM/dd/yyyy",
        "daterange": "MM/dd/yyyy",
        "datetime": "MM/dd/yyyy HH:mm",
        "firstDayOfWeek": 7
      }
    }
  }
}