subsolvedirectives is never used

[DLWoodruff]

We need a hierarchy of solver options and a service function to manage the options. E.g., an EF could look first for EF_solvername but if it is not found, use solvername, etc. DLW has some ideas about this.

Also: many examples (particularly older examples) have something like
options["subsolvedirectives"] = None
but if it was not None, nothing would change. The examples should probably be updated.