Fixed bug with deleting remote balls

How to reproduce:
-Start a two player game
-Have one of the player loose a ball
-The ball will be deleted from Renderer but not from GameManager. This
is because RemoveBall() does not delete items from ballList, this is the
responsibility of DeleteDeadBalls()
-DeleteDeadBalls is called properly for local player balls, the problem
is only with remote balls.

Fix:
-When recieving a Ball kill message, it is killed by calling the
Kill() fcuntion.
-After the ball is killed, the RemoveDeadBalls() function is called to
clean it up.
-Added Renderer output when killing Balls, including a cin.ignore() when
Ball is not found.