Bug 30933: Add lists methods for disowning

Bug 30933: Add lists methods for disowning

This patch aims to tidy things a bit by doing the following changes:

* Koha::Virtualshelf gets the 'transfer_ownership' method
* Koha::Virtualshelves gets the 'disown_or_delete' method
* Koha::Patron->delete gets rewritten/simplified by using
  disown_or_delete

The idea is to capture the current behavior in more fine grained
methods. So current tests should be passing as they do now.

To test:
1. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Patrons.t \
           t/db_dependent/Virtualshelves.t
=> SUCCESS: Tests pass
2. Apply this patches
3. Repeat 1
=> SUCCESS: Tests still pass!
4. Run:
  k$ prove t/db_dependent/Koha/Virtualshelf.t \
           t/db_dependent/Koha/Virtualshelves.t
=> SUCCESS: Tests pass!
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>