Re-architect around pipelines

See merge request rhodes/model_server!58

# Conflicts:
#	model_server/base/accessors.py
#	model_server/base/roiset.py
#	model_server/base/util.py
#	tests/base/test_roiset.py

RoiSet facilitates object detection models

See merge request rhodes/model_server!57

Working functionally but still need to verify that bounding box-generated RoiSet matches content of one with segmentation;

Parameterized deprojection when creating RoiSet from binary mask, including option to pass a channel

Roughed in optional to compare overlaps between two DataFrames, pathway to transferring classification labels