Added fls implementation by Niels Bohr as explained in the following issue...

Added fls implementation by Niels Bohr as explained in the following issue thread: https://github.com/uuvsimulator/uuv_simulator/issues/48, with the main code of the fls contained here: https://github.com/smarc-project/smarc_simulations/blob/master/smarc_gazebo_plugins/smarc_gazebo_ros_plugins/src/gazebo_ros_image_sonar.cpp

. \n\n TODO: Modify FLS to be better representation (current FLS still abuses Depth cam), and integrate FLS into our project environment/requirement better

Add depends to pacakge.xml

# Conflicts:
#	uuv_descriptions/robots/rexrov_test.xacro
#	uuv_sensor_plugins/uuv_sensor_ros_plugins/CMakeLists.txt
#	uuv_sensor_plugins/uuv_sensor_ros_plugins/urdf/sonar_snippets.xacro

Signed-off-by: Will Baker <willcbaker@gmail.com>