Calendar interface for date/DateTime data types

[jonathan-wcc]

Date and DateTime datatypes (i.e. http://www.w3.org/TR/xmlschema-2/#dateTime) would benefit hugely from allowing the user to use a Calendar interface to choose the date.

I.e. something like this: http://javascriptcalendar.org/siteimg/javascript-calendar.png

[ahocevar]

The calendar should be available already, e.g. in the FeatureEditPopup. Where do you see it missing?