Basic power-up system, resized camera, art

Basic power up system can:
-Spawn power-up after semi-random amount of time
-Move power-up in leaf falling pattern
-Destroy and respawn power-up

The system does not yet:
-Interact with the ball or racket to be acquired by the player
-Change or affect the players in any way

-The camera has also been adjusted to make the court bigger and more
spacious.

-Added background art.