Cleaned up BouncyBallPhysics sketch

* Removed deadspeed global as it's no longer necessary, everything comes to a halt naturally;
* Kinetic forces given over serial can only be positive, removed the check for '-' char for Serial.peek();
* Ball class Constructor that sets height can now also set a speed (defaults to zero);
* Renamed several methods to names that fit better to the physics they describe;
* Changes of velocity because of acceleration are handled through direct speed adjustments, not as added kinetic energy;
* Bouncing a ball no longer removes a static 1 Joule of energy from the ball, only elastic losses apply.