Bug 16965: search_related returns an instanciated Koha::Objects-based object

Bug 16965: search_related returns an instanciated Koha::Objects-based object

Koha::Objects->search_related should return a Koha::Objects-based
object.
This search_related method should follow the same rules as the search
method, i.e. take into account what the caller want (scalar or list).
The problem here is that we do not know (in Koha::Objects) what is the
kind of objects we want to instanciate. To know it, this patch adds a
get_object_class, it will return the class of the object and the
resultset Koha::Object-based object.

The drawback of this method is that we will have to keep it up-to-date
every time we add a new Koha::Object class.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>