config persists over restart for study (fix #27)

Current tests show:

* startdate, personid persist over addon enable / disable
  (hard to actually restart fx during testing)
* changes in `_config` persist to "simple-storage"

Assuming `simple-storage` is correct, this is Pretty Good
evidence that all now works as expected.
Removed unused `requireAny` function.

`cfx` path searching makes `requireAny` hard to use, because cfx won't
build unless it can actually find all the modules.

Was full documented, but no tests.
`lifetime(falsy)` still starts a study (fix #30)