Incomplete, but replacing manual status code assertions with assertion methods of TestServerBaseClass

Parameters auto-validates anything ending in accessor_id and model_id; call_pipeline() maps these to objects and sends to pipeline function as dicts of respective objects

Because tests will be run after model_server is installed as a package, they revert to importing model_server.base.*

Separate _put arguments for query and JSON-encoded body data in test client; test case showing pydantic model is required for list args

This reverts merge request !16