getDayOfWeekOfFirstMonthDay(year, month_index) {
        var d = new Date(year, month_index).getDay();
        if (d === 0) {
            d = 7;
        }
        return d-1;
    }
Get day of week (monday-sunday) of first day in month of year
@param  year
@param  month_index (0-11)
@returns  {number} day of week index - 0 (monday) - 6 (sunday)