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

Made a workaround for passing all channels to pixel classifier; stable export script using this from multiposition CZIs

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

Repair automatic session restart, which was causing test client problems; corrected return value of model query

Test covers problem with models being duplicated because of different path specifications; not yet fixed at API level