message: added axis to models.Instrument
diff: @@ -21,6 +21,7 @@ class Instrument:
  self.name = instrument.name
  self.channels = instrument.channels
  self.mount = instrument.mount
  + self.axis = 'a' if self.mount == 'right' else 'b'
  self.tip_racks = [
  Container(container)
  for container in instrument.tip_racks]
  