Changed default step to 1 second

Imo it makes more sense to have the default step set to 1 second, rather than 1 day, doesn't it?

This validator is used by default for DateTime form elements and requires a lot of additional configuration, just to be able to input values with a time part.

Additionally when this validator fails, the form element does not report an error, rather it goes into an infinite loop, but that's another issue.