[ENH] Seeding on the white matter-gray mattter interface

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Here is a first attempt at seeding in the gray matter white matter interface using hidden Markov Random Field models (as implemented in DIPY) on slightly modified anisotropic power maps (no T1 needed). I also set this as the default seeding to see which tests it would throw

Screen.Recording.2024-01-27.at.11.38.56.AM.mov

There are some other minor bug fixes in here:
Fix IFOF color scheme
Throw warning and exit in apply_cmd_to_afq_derivs if you are trying to clobber() a directory that doesnt exist yet

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Should consider trying this instead: #418

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Or use #1129