make dateinput work again by using the fixed name "date" as expected by ...

...the pstruct schema

I don't really understand why the date input was changed from being a simple single input to a mapping, but this change to the template makes it so it actually works.  Without this change you get the following error message:  "Invalid pstruct: {'date': 'Required'}"  (unless, of course, if you happened to name your dateinput field "date")