A class and task that clones a case. (#3826)

Provides `setup:clone_case`, a rake task which produces one or more clones of a participant and all its related persons, participants, and other case-specific records. It also syncs any primary participants to PSC. This task is intended for use in setting up training or QA data.

This branch also includes a fix for [Cases-3848](https://code.bioinformatics.northwestern.edu/issues/issues/show/3848) because it involves a refactoring of `Participant` to share its "importer mode" code with `ResponseSet`.