Change dateparts widget to use type=number

[stevepiercy]

• Adjust test to submit only numbers, but still be an invalid date (2020-02-31)
• Fixes #442

[stevepiercy]

The single failing test should fail, because the original test sent text instead of numbers. Merging.

[stevepiercy]

See https://github.com/Pylons/deformdemo/pull/90