Bug 22812: Use Koha::Subscription in NewSubscription

Bug 22812: Use Koha::Subscription in NewSubscription

Starting to write tests I realize that we are going to add too much
specific logic which is already handled in Koha::Object->store.
The easiest and safe way is to use it :)

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit b41f215bfedbae0898a9291d2f14e2a3dd560049)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>