Add xbox controller mode switch

[KatherineZT]

An xbox controller can already be used to control the motors. The robotic arm can also be controlled using an xbox controller, but with a ROS package that is in another git repository. The rover's pilot should be able to switch between "motor control" and "arm control" with a simple switch on the control portal.

• Add a mat-button-toggle-group on the control portal for control mode switching between "wheels" and "robotic arm"
• Publish to a topic from the ROS_sixi repository and send valid commands to the robotic arm

May be possible :

• Subscribe to a topic from the ROS_sixi repository in order to receive data from the arm (if such a topic exists)