Use old transformer

[jessicaflowers]

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Description of the Change

Replace the new cctbx transformers with the old ones. This required the addition of a few files, _extensions.c and atomsf.py, as well as changes to setup.py to reflect those additions. Minor changes to qfit.py, just to use the old _convert() function that reflects usage of the old transformer.

Release Notes

Revert to using the old transformers

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[natechols]

Instead of deleting the CCTBX code, it would be simpler to just revert 7384c4b2efaa8e03b1af3a4dfc52d5e7bcb5295a