Simulation: underwater environment plugin

[OscarSmiley]

Goal

Research and integrate a gazebo plugin for simulating and underwater environment.
Contenders include but are not limited to:
Underwater Simulator: more developed, limited support, http://www.irs.uji.es/uwsim/
Free Floating Gazebo: more lightweight, https://github.com/freefloating-gazebo

Status

Nothing has been integrated or tested yet.