Crawl github organizations for subdatasets

[yarikoptic]

Original intent is openneurodatasets.

TODOs

• [x] Fix up for recent changes in github helpers "interface" (all protected functions) since ATM isn't usable
• [x] some unit testing (sample invocation datalad crawl-init --save --template=gh org=datalad-collection-1 include=--ds000 exclude= get_data=True drop_data=True metadata_nativetypes=nifti1,xmp,bids; datalad crawl)

Related/discovered issues:

• https://github.com/datalad/datalad/issues/3055 - for now I have disabled aggregation and getting data by default. We will probably do it using some "crafted" procedure (or plugin? or interface? ;)) after crawling update whenever it is necessary
• a number of openneuro datasets do not have data accessible for a number of reasons... do not back referencing here to not agitate west coast developers. update: some were fixed up, some not, some newly broken... nothing for us to do here

[codecov[bot]]

Codecov Report

Merging #28 into master will decrease coverage by 4.09%. The diff coverage is 23.65%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   82.55%   78.46%   -4.10%     
==========================================
  Files          53       57       +4     
  Lines        4214     4593     +379     
==========================================
+ Hits         3479     3604     +125     
- Misses        735      989     +254     

Impacted Files	Coverage Δ
datalad_crawler/pipelines/gh.py	12.50% <12.50%> (ø)
datalad_crawler/pipelines/tests/test_gh.py	61.90% <61.90%> (ø)
datalad_crawler/pipelines/tests/test_xnat.py	54.28% <0.00%> (ø)
datalad_crawler/pipelines/xnat.py	25.41% <0.00%> (ø)

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[yarikoptic]

could and will be improved, will merge as is for now