For lists of domain objects, re-store provides a
dedicated type: ObjectList<T> where T denotes
the domain object class.
An ObjectList is more than just a collection of objects.
In re-store, it embodies the "n"-side of bidirectional 1:n
relations.
For this reason, ObjectList-s update the other relation
endpoint about modifications (add, remove) and vice versa.
The example from the PhoneBook tutorial is the list of
phone-numbers associated with a person (ObjectList<PhoneNumber>).