STY: Normalize to blue and isort

[effigies]

Looking at #1114, I think we're past the days of asking people to follow style guides. Code formatters have gotten a lot better in the last decade, and it makes more sense to just give people the configuration to auto-format.

Here I'm proposing we use blue, which is like black but doesn't insist on double-quotes everywhere.

I'm also suggesting isort just because I've seen a number of PRs where people's editors auto-sort imports for them, so let's just tell their editors what to do.

The style config becomes:

[flake8]
max-line-length = 99
extend-ignore = E203,E266,E402,E731
exclude =
    *test*
    *sphinx*
    nibabel/externals/*
    */__init__.py

[blue]
line_length = 99
extend-exclude = _version.py

[isort]
extend_skip = _version.py
profile = black
line_length = 99

There are some things I want to revert and protect from re-formatting, most notably the NIfTI intent recoder. But on the whole I find very little objectionable and some things look noticeably better. Any objections / other things to revert and protect?

[codecov]

Codecov Report

Base: 92.38% // Head: 92.38% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (69785cd) compared to base (0a6e73e).
Patch coverage: 91.72% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1124   +/-   ##
=======================================
  Coverage   92.38%   92.38%           
=======================================
  Files          98       98           
  Lines       12264    12257    -7     
  Branches     2520     2520           
=======================================
- Hits        11330    11324    -6     
+ Misses        613      612    -1     
  Partials      321      321           

Impacted Files	Coverage Δ
nibabel/environment.py	95.00% <ø> (ø)
nibabel/imagestats.py	83.33% <0.00%> (ø)
nibabel/nicom/structreader.py	100.00% <ø> (ø)
nibabel/nicom/utils.py	100.00% <ø> (ø)
nibabel/onetime.py	90.47% <ø> (ø)
nibabel/pkg_info.py	73.91% <ø> (ø)
nibabel/streamlines/tck.py	99.48% <ø> (-0.01%)	⬇️
nibabel/streamlines/tractogram.py	99.68% <ø> (ø)
nibabel/streamlines/tractogram_file.py	100.00% <ø> (ø)
nibabel/streamlines/trk.py	94.00% <ø> (-0.02%)	⬇️
... and 96 more

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[effigies]

In the absence of feedback, I plan to push on this as time allows and merge when satisfied.

[ZviBaratz]

How do you feel about specifying:

[flake8]
...
per-file-ignores =
    */__init__.py: F401

for init files? Or are there other codes we should be ignoring?

Otherwise, I think it would be great to move forward with this. We can always revert changes in particular files or sections if we find it less readable, and hopefully at some point we will be able to update blue with your PR having been merged. LMK if there's anything I can do to help with this.

[effigies]

Let's break all the PRs...