more sanity checks (BG folder)

[xulman]

• document the purpose of the BG mask file

-> documented in the commit bd6ecb3 .

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• add a code that tests that BG and FG/TRA masks are not overlapping

-> from its early days, there is a log

[INFO] BG&FG overlapping voxels: ....some number...

which essentially does exactly that.

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• consider if there is a way to compute BG automatically from --> e.g. consistent (morphologically opened?) are of pixels that never part of any FG/TRA masks/marker

-> a BGmask creator that can also function as described has been added in commit 43ce09f

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• add "whole embryo detector"