Resources: Added the extraball power sprite to the repo.

gameObjects:
-- Ball: Removed unused starting variables. Added documentation.
-- Brick: Added documentation.
-- ExplosiveBrick: Fixed grammar of documentation.
-- ExtraBallPower: Fixed spawning direction of the new ball. Added documentation.
-- ExtraLifePower: Added documentation.
-- GameObject: Clarified documentation.
-- GhostPower: Added documentation.
-- LoseLifePower: Added documentation.
-- Paddle: Changed name of xDir variable.
-- PointsPower: Added documentation.
-- PowerUp: Added documentation.