Bug 30708: Set default values for items added in batch to a train

Bug 30708: Set default values for items added in batch to a train

Technical notes: Ideally we would have split TrainsFormAddItem to make some part
reusable, but it turned out into a complicated component that would have
been hard to maintain. It seems easier to have two different components.
Ideas to improve this area are welcome!

Sponsored-by: BULAC - http://www.bulac.fr/
Signed-off-by: BULAC - http://www.bulac.fr/
Signed-off-by: Heather Hernandez <heather_hernandez@nps.gov>
Signed-off-by: Laurence Rault <laurence.rault@biblibre.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>