mw.widgets.DateInputWidget: Don't get stuck on today's date if none given

mw.widgets.DateInputWidget: Don't get stuck on today's date if none given

If no date was given, the calendar would select today, but the
DateInputWidget itself would have no value.

However, this made the date picker ignore attempts to actually choose
today: the calendar already had that date chosen, so no 'change' even
was fired, and date input stayed empty.

Change mw.widgets.CalendarWidget not to actually select today's date,
just focus the calendar on it.

Follow-up to 66686f8c5e4df1c2cc94273918b9328269d2ec09.

Change-Id: I3ba064982b045a577209d56a009ad0098c357754