[3pt] Set up Label class

[AkashaRojee]

• Create a Label class with an association to the Item class (in a separate .rb file).

• All Label class properties visible in the diagram should be defined and set up in the constructor method.

• Implement methods:

  • add_item method in the Label 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)

• Add unit tests for all implemented methods.

• The following options should be available:

  • List all labels (e.g. 'Gift', 'New')

• All data should be preserved by saving collections in .json files.