Elevator Test

1. Modify the code to be more readable.
2. Try to convert to object oriented, simplicity & reusability is the main point.
3. Currently, the elevator would run one-by-one, solve the code so those 3 elevator can serve the in a parallel way without conflicting each other when serving on the same floor (1 floor 1 elevator).
4. Fix incorrect Person floor position with the "Waiting" text, that must be a waiting person on specific floor, ready to pickup.
5. Optimize the number of people served by elevator, e.g. move faster and smooth without removing the animation.
6. Shorter time to serve is better.