Update grainstats entry point to work with ImageGrainCrops

[ns-rse]

#1022 restructures from a dictionary to add new classes for image grain crops (ImageGrainCrops).

Subject to...

a) TopoStats saving all of this raw data when saving to .topostats files.
b) updating AFMReader to reconstruct these when loading .topostats files.

...we will then have to update the grainstats entry point to use these.

Currently the tests/run_modules.py::test_grainstats() test is disabled.

The change(s) to make will be...

1. Reconstructing the image_grain_crops (of class ImageGrainCrops and various attributes of different new classes).
2. Passing this into the processing.run_grainstats() function when called from processing.process_grainstats().

For progress see also AFMReader #121.