Multi-group support for MotoPlus motion driver

See changelog in ted-miller/motoman branch.
This is a limitation of the robot controller.  The motion API can control 4 groups (of 8 axes each) on the FS100 and DX200.  This can be any combination of robots or external axes.
The DX100 is actually limited to only 2 groups.  I opted not to put a compiler switch around this definition so as to keep the message size consistent.