class_docstr: Monitor a given trial inside a thread, updating its heartbeat
  at a given interval of time.
  
  Parameters
  ----------
  exp: Experiment
      The current Experiment.
code: def __init__(self, trial, storage, wait_time=60):
      threading.Thread.__init__(self)
      self.stopped = threading.Event()
      self.trial = trial
      self.wait_time = wait_time
      self.storage = storage
  
imports: import threading
label_desc: Use image node_id 1 to create a new TrialPacemaker object from inherited base classes: threading with example: obj = TrialPacemaker(trial, storage, wait_time)