Draft: Fixed datefield validation with min/max date & time

Fix for issue #969.

Tested with this app definition:

name: test
defaultPage: test
pages:
  - name: test
    blocks:
      - type: form
        version: 0.24.13
        parameters:
          fields:
            - type: date
              name: date
              requirements:
                - to: { date.now }
            - type: date-time
              name: date-time 
              requirements:
                - to: { date.now }