Now that RoiSet is in base, remove dependency on ilastik in its test; tests now open segmentation mask from file

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

Validated non-duplication when loading ilastik model with same project file name, irrespective of path formatting

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

Pass notebook filename and not path to load an ilastik model; assumes project files are in conf.server.paths['ilastik']