RF: Rename 'PstBox' to 'Pstbox'

With the old naming scheme, PstBox, convertCamelToSnake would create event constant names like PST_BOX_BUTTON; but this would be inconsistent with
the PSTBOX device name in constants.py. Moving to PST_BOX/Pst_Box would also seem rather awkward, so Pstbox is probably the best choice for now.