Nibabel can load MINC, but now we need an API to get the axis names for
MINC, otherwise, the axes can be anywhere, but are most likely to be in
the opposite order to the ones the NIfTI needs. Raise an error until we
have worked out how to do this right.
The command line utilities nipy_tsdiffana and nipy_diagnose guess the
slice axis for Analyze-like files (like Nifti) - so the `screens`
function doesn't need to do that, and it doesn't match the API for --
say -- `pca_image`. So deprecate the slice axis guess in `screens` and