Added the TimerListener private class to SimulationController. This
serves as an action listener for the Timer that I also added to
SimulationController. Added an override to the JPanel's paint() method
and just told it to repaint the ViewPanel. Added a method call to Ball's
move() method in ViewPanel's paint() method to move the ball every time
the panel is repainted. Changed the x and y velocities of a Ball
instance.
Added some comments and deleted the System.setProperty() call, as this
won't work in the current version of Java.