Integrate a PID feedback loop to the motor driver

[dave]

The motor driver rotation API is currently very crude, and as a result fairly inaccurate. We should integrate a PID loop to slave the motor output power to the target tacho count, so as to have smooth and controlled transitions between states.

Dave has some proof of concept PID implementation hacked into the motors driver, and seems to remember it actually turned out to be a PI controller. The most annoying thing is that he stupidly lost the Perfect(tm) calibration settings for the control loop, so all the calibration work will have to be redone.