Add a method for exporting/importing preferences

It would be nice if there was a quick way to export and import preferences from one Arbitrator instance to another. We basically already have the export functionality set up, we just need to make it more explicit with an import and export command set. Further, this will set us up with a method for synchronizing across multiple Arbitrator instances (if we ever want to do that).

Start by locating the existing preference export functionality and the command entry points in the repository. Trace how an Arbitrator instance currently stores and exports preferences, then define the import and export command behavior needed to move preferences between instances. Done means both commands provide a usable transfer path and preserve the existing export behavior.

Written by the indexing model from the issue text.