Adjusting plot in `DQ_SerialManipulator` and subclasses to compensate for 'set_effector'.

[mmmarinho]

Hello, @bvadorno,

Currently, the plot method in DQ_SerialManipulator is correctly taking into account the transformation induced by set_effector() when plotting the end-effector's frame, but the frame is floating without any visible connection with the rest of the robot.

matlab/robot_modeling/DQ_SerialManipulator.m

Line 337 in 203c833

function plot(robot,q,varargin)

I think that, initially, we can consider just drawing a straight line between the last robot's frame and the end-effector's frame to represent this transformation, although in many cases that straight line would not be a good representation of the end-effector.

Maybe for 20.10 we can consider more interesting alternatives.