Beta 1

In this beta version:
* Follow Object-Oriented concept. (Bag, Ticket, LockerSystem, Concierge)
* Implement storeBag and unstoreBag function.  

# What's next
* Add update function to Concierge in order to maximize utilization of locker system.
* Add listener to LockerSystem and decide when to update current lockers (reorder bags according to their sizes).





*** Caution: For convenient testing, set maximum lockers to 9 (3/3/3)