Lots of motor stuff.

@rhempel, I have made quite a few changes to various motor-related things. Some of it is in tacho_motor_class and ev3_tacho_motor, so I wanted to give you a chance to review it before I merge it. This would be a good change to try out your motor test scripts to make sure I didn't break anything.

I did make one purposely breaking change to the tacho-motor class. The devices are now named `motor0` instead of `tacho-motor0`. This is for consistency with the other new motor classes that I have introduced.