Stop the servo suddenly jumping when it goes out of the deadzone in one direction

Servo value normalisation should result in a value between -1 and 1. This fixes an issue where the numerator can be larger than the denominator resulting in a value > 1 when raw servo values are at their minimum value. The side effect of this is that there is a noticeable jump in the scaled value when moving the servo in one direction resulting in a sudden servo arm jump.

The calculation can be verified by considering a raw = 1000 and a raw = 2000 with center = 1500 and deadzone = 50. Prior to this change you would end up with a 1000 - 1500 - 50 / 1500 - 1000 - 50 = -550 / 450.