Repurpose `orchestrator.py` code for plugins and tests

The previous `orchestrator` module (now `wes_orchestrator`) included a lot of additional logic for interacting with WES (and to a lesser extent, TRS). Most of this logic should instead be handled as part of classes or controllers for tests and test plugins.

The orchestrator itself should be responsible for knowing how to `run` and perform other scheduling-like operations with "tests" (as instantiated from specific plugins).