class_docstr: Identify pairs whose indicator exceeds some threshold and save them on temp.
  
  Args:
      * threshold (float): The threshold to use for the indicator between pairs
      * indicator_name (str): The name of the indicator data set
  Sets:
      * pairs
code: def __init__(self, threshold, indicator_name):
      super(PairsSignal, self).__init__()
      self.threshold = threshold
      self.indicator_name = indicator_name
  
imports: from copy import deepcopy
  from future.utils import iteritems
  from datetime import date
  import pandas
  import numpy
  import bt
label_desc: Use image node_id 1 to create a new PairsSignal object from inherited base classes: bt with example: obj = PairsSignal(threshold, indicator_name)