first pass at adding water_depth passed in ssp message.

Breaking Changes

• adds new field to ros_acomms_msgs/SoundSpeedProfile: water_depth

New Features / Improvements

this needs to be tested. I added a lot of try/catch handling to make this fallback to old handling

• sim_transmission_loss sets depth in bellhop env on each ssp update when rosparam ~use_water_depth_from_ssp is set to True (by default this is False to preserve the old behavior).
  • when ~use_water_depth_from_ssp:True
    • and ssp_message.water_depth > 0, env['depth'] = float(ssp_message.water_depth)
    • else, env['depth'] = float(ssp_message.depths[-1])
  • when ~use_water_depth_from_ssp:False, the bellhop env['depth'] is left with the value at at launch (self.water_depth)