Split out patch/patch mask creation for file export; implemented and test accessor abstraction for patch arrays

Updated existing export jobs with new argument names and model objects that are initiated outside workflow scope

Lifted z-stack assertion, made util.loop_workflow more generic e.g. for on-the-fly data conversion tasks

Lifted z-stack assertion, made util.loop_workflow more generic e.g. for on-the-fly data conversion tasks

# Conflicts:
#	extensions/chaeo/examples/transfer_labels_to_ilastik_object_classifier.py