bug fixes of gw2wannier90.py & k_mapper.py

[qiaojunfeng]

This pull request contains:

1. bug fix for gw2wannier90.py when transforming spn file, originally proposed in Issue in formatted spn format #293
2. transforms gw2wannier90.py & k_mapper.py to python 3 syntax.
3. scripts formatted by yapf
4. minor fixes to make the script easier to use
5. add an option write_formatted to select whether to output formatted or unformatted files when the input files are unformatted
6. add non-collinear support for UNK files

Have been tested on example23 with and without spin-orbit coupling, works fine on both formatted & unformatted spn, uHu, uIu, and UNK files, and non-collinear UNK files.

[codecov]

Codecov Report

Merging #294 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           develop    #294   +/-   ##
=======================================
  Coverage     65.6%   65.6%           
=======================================
  Files           29      29           
  Lines        17938   17938           
=======================================
  Hits         11768   11768           
  Misses        6170    6170

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[giovannipizzi]

@AntimoMarrazzo @stepan-tsirkin could you give a look to this PR and confirm that for you it's ok? Thanks!

[stepan-tsirkin]

It has been a while since I wrote the code, and I have not used it almost since then. The changes look correct, and I believe that Junfeng tested the script. I agree that there was a bug in writing spn file.
Thank you for fixing the bug and decorating the script. I am glad that my old script has its own life.

[AntimoMarrazzo]

OK to merge.