[1pt] [Team member #2] Implement methods

[Mike47ip]

- add_item method in the Genre class
    - should take an instance of the Item class as an input
    - should add the input item to the collection of items
    - should add self as a property of the item object (by using the correct setter from the item object)
- can_be_archived?() in the MusicAlbum class
    - should override the method from the parent class
    - should return true if parent's method returns true AND if on_spotify equals true
    - otherwise, it should return false