Bug 8428 - can't save contracts

When I replaced the old calendar widget with the jQueryUI version
we lost a JavaScript function which is required by a couple of
pages: Date_from_syspref. This patch adds the function back
to the calendar include and corrects variables in the two
affected templates to make it work again.

To test:

- create a new contract. Submitting should work properly and
  without JavaScript errors.
- Open the serials claims page (serials/claims.pl) and filter
  the results by date. Submitting the filter form should
  work properly and without JavaScript errors.

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Both tests passed.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>