Added interface for the Gazebo 1.9 onwards on the complete urdfs from JHU

Hey Zihan. 

I have removed the previous dv_gazebo_plugin package as that was outdated and no longer worked, ros groovy onwards. I have added a new gazebo interface that is based on the latest gazebo platform and compatible with ros-hydro onwards. This interface relies on the JHU's complete urdfs and not on the urdfs we had. I have made the necessary modifications to the mtm.urdf.xacro file, these changes are totally independent of the previous functionality and do not affect any other package or usage at all. I have tested this at my end.

You can now run the gazebo simulation of the MTM and I have provided the ros_topic interface for controlling all the joints. Based on the rough and wrong dynamic values in the mtm.urdf.xacro file, the response can be seen quite well and we can clearly see the dynamic oscillations and damping of joints when a new values is set of the joint. We can use this to develop an accurate dynamic model. I shall add a documentation .md file pretty soon. Hold on as I add a PSM gazebo interface soon enough as well.

Thanks,
Adnan Munawar.