Bug 25789: Don't allow past date as holds expiration date

Bug 25789: Don't allow past date as holds expiration date

When editing existing holds expiration date it's possible to select
past date from datepicker. This patch changes expiration inputs class
as "datepickerto" to make past dates unselectable.

To test:
1.  Find item with holds
2.  Edit holds expiration date
=> Note that past dates are selectable
3. Apply patch
4. Edit again
=> Past dates are no longer selectable

Sponsored-by: Koha-Suomi Oy
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>