User empty object print ValueError

[Bachibouzouk]

issue: When a user object is empty cannot be printed due as the repr method uses the save() method to print the properties of the users, which raise Exception in case no appliances are added to the user.

solution: in case save() methods returns an exception, the function prints the user_name, and user_num with a message to mention no appliances are assigned to the user object yet.

additional:

• found a bug in __eq__ method of Appliance class and fixed it
• add the possibility for a user to pass directly Appliance instances to the add_appliance method of the User class
• add two new test files

[Bachibouzouk]

@mohammadamint - I added a new method and fixed a bug in Appliance comparison I found while playing around with Appliances to test your fix