Multi-group support for MotoPlus motion driver

See changelog in ted-miller/motoman branch.
Does this mean that only `MOT_MAX_GR` (i.e. 4) robots can be controlled with a single controller?  Is this a controller limitation or did you set this to limit the communications traffic?

The ROS-I REP describes these messages as being dynamic (i.e. the number of robot groups could change).  Is there a reason that you decided not to do this?  There was some concern about communications overload.  Did you see this?