gpsToB.py

The GPS navigation test is inconclusive.

The process is to roslaunch swiftnav_ros swiftnav_ros.launch, rosrun gravl gpsToB.py, and drive around the orange location marker close to the freight containers. The results are bearings towards the circle which trend properly, as in driving around the circle creates a smooth transition from negative to positive values on roughly the correct side of the marker. The error seems to be roughly 20 degrees off, so I suspect that the north indicator on the marker is oriented to magnetic north, wheras the tractor's bearing indicator is oriented to true north, but that is inconclusive until I talk to the coordinator.