Fixed setting attributes on the 5 readonly @property

member_ids, short_id, list_id, board_id, and description
are readonly properties.

Changed to direct access the underlying variables:
 - idMembers
 - idShort
 - idList
 - idBoard
 - desc
Refactored JSON deserialization for every class

- Refactored deserialization into class method 'from_json' for every class
- Replaced some simple for loops with list comprehensions
Changed the due_date format in Card

YYYY-MM-DD was the chosen format due to the original intention
observed in def set_due, which was different from 'self.due' assignment
in Card.fetch.  For practical reasons, YYYY-MM-DD was chosen.

- Due date of Card is in YYYY-MM-DD format.
- Extra test case was added for set_due on a card.