Bug 20472: Add new fields article_requests.format and urls

Bug 20472: Add new fields article_requests.format and urls

The field 'format' will allow to make a distinction between requests for
photocopies and digital scans.
The field 'urls' will be used to save the URLs that allow the client to
download the scanned materials.

Test plan:
Run new install or upgrade existing install with atomic update.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>