public void shiftCurrentMonth(int deltaMonths) {
        CalendarUtil.addMonthsToDate(currentMonth, deltaMonths);
//        refresh();
    }
Shifts the currently specified date by the given number of months. The day
of the month will be pinned to the original value as far as possible.

@param deltaMonths - number of months to be added to the current date
stroom-core-client-widget/src/main/java/stroom/widget/datepicker/client/DateTimeModel.java