Updated traversal code -- needs proper testing

[gklyne]

Changes to the parameter/key names for defining a graph traversal, per oerc-music/meld-testing-ssi3#1 (issue set up as TODO in a different repo).

I've also changed the registerTraversal function to (a) log a message if any unrecognized parameter/key names are used (including the old names), and (b) if the old names are provided by a caller, to map them to the new parameter names.

I've checked that the code compiles/builds, and that hello-meld-2 and hello-meld-3 work with these changes. I'm raising this as a PR mainly to invite review and comments.

[gklyne]

I've also run npm run build to create files in the lib/ subdirectory (compiled JSX, etc.), which accounts for the number of new files.

[gklyne]

I've also added a log message if graph traversal encounters a non-JSON file

[gklyne]

Bug fixes applied - branch now works with 'hello-meld-3', which does rudimentary graph traversal.

(At least, it does for me when run with a local copy of this code.)