message: Adds logging to session.py
diff: import ast
  +import logging
  from copy import copy
  from datetime import datetime
  from functools import reduce
  @@ -10,6 +11,7 @@ from opentrons import robot
  from .models import Container, Instrument
  +log = logging.getLogger(__name__)
  VALID_STATES = {'loaded', 'running', 'finished', 'stopped', 'paused'}
  @@ -145,16 +147,19 @@ class Session(object):
  return self
  def stop(self):
  + log.info("Stop Initiated")
  robot.stop()
  self.set_state('stopped')
  return self
  def pause(self):
  + log.info("Pause Initiated")
  robot.pause()
  self.set_state('paused')
  return self
  def resume(self):
  + log.info("Resume Initiated")
  robot.resume()
  self.set_state('running')
  return self
  