ENH: Add optional session distinction to wrangler

[mgxd]

In the same vein as nipreps/niworkflows#678

[codecov-commenter]

Codecov Report

Merging #261 (324d89b) into master (d245dfd) will increase coverage by 4.26%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #261      +/-   ##
==========================================
+ Coverage   83.09%   87.35%   +4.26%     
==========================================
  Files          25       25              
  Lines        1851     1850       -1     
  Branches      278      278              
==========================================
+ Hits         1538     1616      +78     
+ Misses        281      204      -77     
+ Partials       32       30       -2     

Flag	Coverage Δ
travis	83.08% <100.00%> (-0.01%)	⬇️
unittests	87.24% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
sdcflows/utils/wrangler.py	97.53% <100.00%> (-0.04%)	⬇️
sdcflows/workflows/outputs.py	93.54% <0.00%> (+1.61%)	⬆️
sdcflows/interfaces/reportlets.py	89.83% <0.00%> (+1.69%)	⬆️
sdcflows/interfaces/bspline.py	87.44% <0.00%> (+4.18%)	⬆️
sdcflows/interfaces/fmap.py	87.35% <0.00%> (+14.94%)	⬆️
sdcflows/workflows/fit/syn.py	69.82% <0.00%> (+21.30%)	⬆️
sdcflows/utils/phasemanip.py	94.02% <0.00%> (+28.35%)	⬆️

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[mgxd]

this will be needed for nipreps/nibabies#193 - could I get a quick review?

[effigies]

Bumping CI to make sure things haven't broken...

[effigies]

And naturally they broke.

[mgxd]

Yeah I would guess master is broken - this is what I was trying to fix in #269