Adds support for multi-groups

This pull-request results from the implementation that adds support for multi-groups to the MOTOMAN robots.

This was succesfuly tested on a Motoman SDA10F and on a Motoman SIA10F for backwards compatibility purpose.

The modifications intend to be compliant with the REP-I001 : 

https://github.com/ros-industrial/rep/blob/master/rep-I0001.rst