Add software killswitch control

[Thinking-Dragon]

For this item to be accepted as complete :

• A component called killswitch must be created ;
• ROSService must be injected into the component ;
• The component must get a reference to the topic called /killswitch_state (message type is std_msgs/Bool) ;
• The component's view must contain a button ;
• The button must initially be red ;
• When the button is clicked (red), it must become black ;
• When the button is clicked (black), it must become red again ;
• When the button is clicked (red), a message with value true must be published on /killswitch_state ;
• When the button is clicked (black), a message with value false must be published on /killswitch_state.