User.java
- Added getId()

UserFactory
- Added simple constructor (to be modified further)
- Added newUser(), getUser(String), getUser(int) for interaction with
the List<User>
- Added update(User, User) to update/replace an item in the List

- Added bookStatus() that will help main program to determine if the
books are not past due
- Added returnBook(int) to remove the returned book from the List
- Fixed List<int> as List<Integer>
- Added import java.util.* for List and ArrayList
- Fixed status with status()

User.java is added with basic / expecting data and functionality