[WIP] adding mapping and submitter to enh/workflow syntax

[djarecka]

I've started adding my mapping and submitter to #2629. I didn't know how to merge NewNode with my submitter without creating an extra class NewNodeBase and treating NewNode as a wrapper that runs nodes's interface.

For now, I only added things related mapper, ignored join and joindByKey. Would like to get feedback first.

I will be adding more tests (to shows mapping), working on NewWorkflow class.

[codecov-io]

Codecov Report

Merging #2638 into master will decrease coverage by 3.5%.
The diff coverage is 70%.

@@            Coverage Diff             @@
##           master    #2638      +/-   ##
==========================================
- Coverage    67.6%   64.09%   -3.51%     
==========================================
  Files         340      343       +3     
  Lines       43003    43479     +476     
  Branches     5321     5448     +127     
==========================================
- Hits        29073    27869    -1204     
- Misses      13231    14530    +1299     
- Partials      699     1080     +381

Flag	Coverage Δ
#smoketests	?
#unittests	64.09% <70%> (-0.96%)	⬇️

Impacted Files	Coverage Δ
nipype/info.py	88.05% <ø> (-5.98%)	⬇️
nipype/pipeline/engine/__init__.py	100% <100%> (ø)	⬆️
nipype/exceptions.py	100% <100%> (ø)
nipype/pipeline/engine/submitter.py	45.45% <45.45%> (ø)
nipype/pipeline/engine/workflows.py	71.18% <66.66%> (-7.9%)	⬇️
nipype/pipeline/engine/state.py	73.17% <73.17%> (ø)
nipype/pipeline/engine/auxiliary.py	76.97% <76.97%> (ø)
nipype/pipeline/engine/workers.py	93.33% <93.33%> (ø)
nipype/interfaces/nilearn.py	40% <0%> (-56.67%)	⬇️
nipype/utils/spm_docs.py	25.92% <0%> (-44.45%)	⬇️
... and 56 more

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