Integrate new confounds infrastructure

[oesteban]

This issue corresponds to PR #1487.

Dependencies:

• Get [ENH] CompCor enhancement nipy/nipype#2878 finally merged, via Update Nipype's regress_poly and cosine_filter to output NaNs #1539, and after tests on [WIP][ENH] Confound model enhancement #1487 pass.
• Pin niworkflows to the new DerivativesDatasink (Refactor DerivativesDataSink: write metadata sidecars niworkflows#308) and write integration code to write sidecars (relates to -if not fixes- Update Confounds #1301).
• Address Update CompCor plotting to allow getting NaNs niworkflows#320
• Finish up [WIP][ENH] Confound model enhancement #1487 now ENH: Confound model enhancement #1586

[oesteban]

@rciric you can pin

git+https://github.com/oesteban/niworkflows@72822f2a8dc5e77c3b989b912ba19aa34524dd7f#egg=niworkflows

to check the new meta_dict input of DerivativesDataSinks.

[effigies]

I think this is done?

[oesteban]

Opened a follow-up here: #1616