Path execution

Added code to (hopefully) stop a train at the target location. Finds the last sensor in the path, such that the distance from the sensor to the destination is greater than the trains stopping distance. After hitting the sensor, adds a small delay based on the trains current velocity. After delaying, sends the stop command and the train should stop at the destination.

Also added an rs command to reset the track, and updated the pa command to allow parsing of sensor names, e.g. D12