Mary catching up with Tristan's changes to move the directory specs back into individual scripts, etc.

Tristan, I'm finally catching up with these changes to "build bricks, not houses" and so on.  I'm issuing a pull request, so that I can merge your changes into my fork.  However, I do have a concern about how this extensive "Rewrite of the start-up wizard ..." links the specification of pathnames to the segmenter's "initials" (and hence to a segmenter-specific version of a separate Praat script that will then need to be copied into each segmenter's working directory whenever changes are made) instead of to the segmenter's "location" for the current session (which is a more dynamic specification and can include differing roles, such as MB acting as a developer without being logged onto the UMN server by a slow internet connection versus MB acting as a segmenter to test changes).