class_docstr: A negotiation teacher that loads the CaSiNo data from
  https://github.com/kushalchawla/CaSiNo.
  
  Each dialogue is converted into two datapoints, one from the perspective of each
  participant.
code: def num_episodes(self):
      return len(self.episodes)
  
imports: from parlai.core.teachers import Teacher
  from .build import build
  from parlai.utils.io import PathManager
  import json
  import os
  import random
  import copy
label_desc: Use image node_id 5 for calling the CasinoTeacher obj's underlying member method code with example usage: obj.num_episodes() and returns: len