Bug 37480: Make addroutingmember use Koha::Subscription::Routinglists

Bug 37480: Make addroutingmember use Koha::Subscription::Routinglists

This patch rewriteis the method so it relies on Koha::Object-based
classes instead of the old way.

To test:
1. Run:
   $ ktd --shell
  k$ prove t/db_dependent/Serials.t
=> SUCCESS: Tests pass!
2. Apply this patch
3. Repeat 1
=> SUCCESS: Tests pass!
4. Run:
   $ git grep addroutingmember
=> SUCCESS: It is only called on a single .pl file which doesn't care
about the return value. Neither the tests care.
5. Sign off :-D

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>