This reverts commit 3332573d.

Separate out method to read each accessor from file, so that this can be overridden in subclasses if needed

Deserialization does not solve deprojection a second time; a deprojected RoiSet is serialized as 3D.  Tight patch mask format depends on dimensions of ROIs themselves, so 2d PNGs are possible in a 3D set if no ROI is thicker than 1

Applied same optimization to binary mask computation, but this still his memory issue on large dataset

Gradually handling three different cases of RoiStack: pure 2d, pure 3d, mixed (3d stack, 2d deprojected object IDs)

Parameterized option to create unique subdirectory for each RoiSet, but this still isn't propagating to dataframe called in .serialize