Begin classes for 3D animation of circuit.

Design:
Pressing "Animate Model" seta two flags, animating and newAnimation.
If both flags are set, the draw loop instantiates an object of type Animation.
newAnimation is then set to false. While animating is true, the draw
loop calls displayAnimation(). This in turn
causes the Towers (at the junctions) and the Walls (for each component)
to draw themselves. It also makes a set of balls start moving on
the tops of the Walls at speeds proportional to the currents in
the corresponding components.

In this version, the overall class structure is laid out and
the Tower class is implemented to display the Towers.
Draw 3D walls.
Add moving balls/charges.

-Animation does appear to be CPU intensive. Computer fan turns on shortly
after animation begins.

-One bug still evident: Sometimes the perspective appears to be closer
(more positive z) than other times. Seems correlated with when you try
to "Animate Model" before the animation window has been setup and turned
gray.
Improve ball animation.

-In previous version, when ball reached end of a wall, it disappeared
then reappeared when another wall was ready for it. The balls now
appear stationary at the top of a tower while they are waiting to
enter the next wall.