[1.5pt] TM#2 Implement methods

[Wineshuga]

• 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