Bug 24446: Update StockRotationItem to use daterequested

Bug 24446: Update StockRotationItem to use daterequested

This patch updates the stockrotation functionality to utilise the new
branchtransfers.daterequested field to more accurately track the state
of stockrotation transfers.

We also opt to start using the new Koha::Item and Koha::Item::Transfer
methods to achieve this goal.

Test plan
0/ Setup stockrotation and configure some rotas and assign items to
them.
1/ Run the stockrotation cronscript
2/ Check the database for branchtransfers initiated by stockrotation and
confirm that that now populate the daterequested field and not the
datesent.
3/ Run the stockrotation tests and verify they pass
4/ Signoff

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