old_contents: 
  class Signals(object):
  
      DOORBELL = "doorbell"
      PICTURE = "picture"
      PICTURE_REQUEST = "picture_request"
      SLACK_MESSAGE = "slackmessage"
      UNLOCK = "unlock"
      UNLOCK_HISTORY = "unlock_history"
      UNLOCKED = "unlocked"
      LOCKED = "locked"
      CLEANUP = "cleanup"
      EXIT = "exit"
  
  
  class Senders(object):
  
      SLACKBOT = "slackbot"
new_contents: 
  class Signals(object):
  
      DOORBELL = "doorbell"
      PICTURE = "picture"
      PICTURE_REQUEST = "picture_request"
      SLACK_MESSAGE = "slackmessage"
      UNLOCK = "unlock"
      UNLOCK_HISTORY = "unlock_history"
      UNLOCKED = "unlocked"
      LOCKED = "locked"
      CLEANUP = "cleanup"
      EXIT = "exit"
      AUDIO_REQUEST = "audio_request"
      AUDIO_CANCEL = "audio_cancel"
  
  
  class Senders(object):
  
      SLACKBOT = "slackbot"
subject: add signals (#24)