Robot should stop braking after motion stops

[andrewda]

Currently the robot stops braking after 5 seconds of disable. We should have it stop braking after the robot stops moving in disabled (which we can see given the encoders' values).

[snowsignal]

@andrewda, I can fix this.

[snowsignal]

Would it make sense for me to spawn a thread that has a while loop running waiting for the encoders to indicate the robot has stopped?