Fix arbitrary dates Period fields activation

Following the replacement of the jscalendar date picker by jQuery (see
issue 0020040), the from / to date input fields are not activated when
selecting Arbitrary Dates period.

This fixes the markup generated by Period.php to add the calendar icon
as well as the javascript that controls the fields's activation.

Using default date format (normal_date_format) for date picker fields
instead of hardcoded YYYY-MM-DD.

Fixes 0025681

Original 2024 commit adapted following rebase to master and resolution
of merge conflicts caused by introduction of datetimepicker API."