Added option to automatically rotate patches in a nonuniform list such that height is always greater than or equal to width; this is a big data reduction for collections of elongated patches

PatchStack remembers crop boundaries of individual patches if created from list of non-matching patches

This reverts merge request !16

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

(1) slicing to a single-channel image now returns its own accessor object; (2) channel slicing now happened at image accessor level, i.e. model is agnostic; (3) TIFF export is now a utility method, not a subclass of accessor