merge kill_switch changes from the pr branch to master
merge kill_switch changes from the pr branch to master

This is the trigger code to start the state_machine running when the
kill_switch is pressed.  Missing from master.
ProgrammingRobotsStudyGroup/robo_magellan,ProgrammingRobotsStudyGroup/robo_magellan,ProgrammingRobotsStudyGroup/robo_magellan,ProgrammingRobotsStudyGroup/robo_magellan