[GSOC-52] Migration of rexov model

[rakeshv24]

This PR introduces the migration of rexrov model. The following changes have been made:

1. Removed all uuv_simulator plugins.
2. Converted xacro and urdf model files to sdf.
3. Added buoyancy, thruster, and hydrodynamic plugins.
4. Tested in dave_ocean_waves.world

Note: The added mass values for the model do not seem correct and cause the simulation to crash. Therefore, we have used values of LRAUV in their place for the hydrodynamics plugin.

[rakeshv24]

@woensug-choi Thank you for the review! I have addressed all the comments.

Imu sensor plugin not included model.sdf

The issue was not actually with the plugin as it already existed. Rather, I had to move the following snippet inside the link for base_link:

<sensor name="imu_sensor" type="imu">
  <always_on>true</always_on>
  <update_rate>1000.0</update_rate>
  <topic>imu</topic>
</sensor>

Collision model

Yes, it was also defined this way on the original dave repo. However, after fixing the tag warnings, the collision model looks much better!