Calculate distance over ground between waypoints

[smwoodman]

Currently, esdglider calculates a distance_over_ground variable between each m_lat/lon point for each of the raw/eng/sci timeseries, using the relevant pyglider function.

For the raw timeseries, it would be nice to add a distance_over_ground_gps, which would contain the great circle distance calculated by gsw.distance. This would probably be more accurate for the total distance traveled by the glider calculations for the post-deployment reports.

[smwoodman]

Sam to investigate: why does c-proof use 'waypoint_latitude', from c_wpt_lat? Is this also what socib uses?