add TestMovie tests

TestMovie class only contains setter and getter test methods : Movie class
doesn't have specific behavior different to Item class.
Item class and subclasses destructor bug has been fixed : the problem was
the deletion of a polymorphic subclass (for example Item* referencing a Movie*)
that didn't call the subclass destructor (only the Item destructor is called).
The solution is to put the Item destructor virtual (this allow both super and
subclass calls).
TestFolder class has been created, test_destructor and associated MockItem has
also been created (Mocking Item class was useful to register if the destructor
method had been called without modifying Item class).