Repository Pattern

[gzt5142]

Exploring the notion that we should take the list of sources as a JSON, TSV, or other source rather than the relational database.

Refactor to use a repo pattern where the source can be plugged in... making the main business logic adapt to an interface rather than a db-specific implementation.

Initial testing successful -- and it has the side benefit of moving some source-specific functions into the object itself (because it's not tied to the ORM).

Proof-of-concept is done; refactor CLI to make use of it.