Create Kill Switch node

[Thinking-Dragon]

For this item to be accepted as complete:

• A new package must be created under /killswitch directory ;
• A node must be created in the new package ;
• The node must contain a subscriber to a topic called /killswitch_state ;
• The node must have a parameter called killswitch_pin ;
• The node must have a parameter called killswitch_pin_default_value ;
• The subscriber must expect messages of type std_msgs/Bool ;
• When a message is received, the value of the GPIO pin with id killswitch_pin must be set to the value contained in killswitch_pin_default if the value of the message is false.

For example, if killswitch_pin is 8 and killswitch_pin_default_value is false, then:

1. If a message with value true is received, GPIO pin 8 must be set to VCC ;
2. If a message with value false is received, GPIO pin 8 must be set to GND.

And, if killswitch_pin is 8 and killswitch_pin_default_value is true, then:

1. If a message with value true is received, GPIO pin 8 must be set to GND;
2. If a message with value false is received, GPIO pin 8 must be set to VCC.