Bug 25755: Add Koha::Item->request_transfer method

Bug 25755: Add Koha::Item->request_transfer method

This patch adds the request_transfer method to the Koha::Item object.
The new method requires `to` and `reason` parameters and will throw an
exception if an active transfer request is found on the item.

Test plan
1/ Run the included updated tests in t/db_dependent/Koha/Item.t
2/ Verify the tests pass
3/ Signoff

Signed-off-by: Kathleen Milne <kathleen.milne@cne-siar.gov.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>