If events TSV file doesn't exist when you go to edit it, then export stim for...

If events TSV file doesn't exist when you go to edit it, then export stim for that processing element. (#157)

* v1.71.1

-- In TreeNodeClass.m, if events TSV file doesn't exist when you go to edit it, then export stim for that processing element.
-- Minor formatting to make git merging smoother