Mnt/fsl package

See merge request fsl/fslpy!290

sense I guess

packages to preserve compatibility with python 2. But py2-compat is no longer
a goal, so we can now use native namespace packages.

Bf/mesh

See merge request fsl/fslpy!288

Rf/bids

See merge request fsl/fslpy!287

"T1w.json" is a valid sidecar file

metadata file name, as files within a BIDS data set may be sym-linked from
another file/directory structure (e.g. datalad/git-annex)

Mnt/deprecations

See merge request fsl/fslpy!286

Mnt/warnings deprecations

See merge request fsl/fslpy!285

fslpy for the most part, so are being moved to fsleyes-widgets

atexit (settings)

Enh/taskthread

See merge request fsl/fslpy!283