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.*

Adapted base segmentation worklow and API endpoint for generic semantic segmentation model; made dummy model this type too

Implemented workflow and endpoint for two-stage (px -> ob) classification in ilastik; tests pass and image data is correct