[0.5pt] Implement all methods: Group task

[ciraganenicole]

Implement methods:

can_be_archived?() in the Item class

• should return true if published_date is older than 10 years
• otherwise, it should return false

  move_to_archive() in the Item class

• should reuse can_be_archived?() method
• should change the archived property to true if the result of the can_be_archived?() method is true
• should do nothing if the result of the can_be_archived?() method is false