Arm pov mount

These changes add the Point Of View camera and mount as an urdf.xacro and mesh, allowing them to be added to the youbot urdf.

This is for the issue mas-group/mas_industrial_robotics#39.
This is required for moriarty/mas_industrial_robotics@778f091980215a4e01584cb67d02a65f9f4123eb to be merged