auv

For support purposes it is good to know where the fences are (polygon, circular, inclusion/exclusion) so we should log these somehow. Perhaps when the log file is first started.

This comes from this discussion https://discuss.ardupilot.org/t/no-polygone-fences-in-the-dataflash-logs/82566/2

As verbally discussed, ocean pressure, added in osrf/lrauv#91 to TethysCommPlugin in the interest of time, should be extracted into its own custom sensor, along with other science sensors in ScienceSensorsSystem.cc, for upstreaming to ign-gazebo.

Note that until longitude/latitude are implemented, the output is meaningless, because pressure is computed from latitude and depth.

Science se