[Feature] Run cell detection on subvolume of an image and not just select z planes

[IgorTatarnikov]

Is your feature request related to a problem? Please describe.
Currently, cellfinder only supports restricting the search space by the start and end plane. Sometimes, it may be necessary to restrict the search space in plane as well (e.g., only run detection in (:, 100:400, 200:500) (z, y, x))