Give Date Edit alternative calendar
The WDateEdit provides a calendar picker;
WCalendar* Wt::WDateEdit::calendar() const
It would be nice if we could give the WDateEdit a calendar that we wish to use instead;
Wt::WDateEdit::WDateEdit( std::unique_ptr<WCalendar> calendar )
This way we can have our own calendar as a picker, rather than the default Wt calendar.