Added robot namespace to gui of rqt_joint_trajectory_controller

[etsiogas]

Mainly useful in multi-robot situations where multiple instances of rqt_joint_trajectory_controller run in different namespaces. Prevents confusion by showing the correct robot namespace to choose from the "controller manager ns" dropdown menu in the controller's window.

[bmagyar]

I've tested this with the following:

<launch>
  <group ns="hola">
    <node name="rqt_jtc1" type="rqt_joint_trajectory_controller" pkg="rqt_joint_trajectory_controller"/>
  </group>
  <node name="rqt_jtc2" type="rqt_joint_trajectory_controller" pkg="rqt_joint_trajectory_controller"/>
</launch>

When using a dummy single robot setup, copy the robot description over to the namespace as well like so:

$ rosparam get /hola/robot_description

Proof by screenshot: