ENH Add 3dZcat and 3dZeropad

[emdupre]

Changes proposed in this pull request

• Create nipype wrapper for the AFNI command 3dZcat
• Create nipype wrapper for the AFNI command 3dZeropad

[codecov-io]

Codecov Report

Merging #2090 into master will increase coverage by 0.02%.
The diff coverage is 93.1%.

@@            Coverage Diff             @@
##           master    #2090      +/-   ##
==========================================
+ Coverage   72.14%   72.16%   +0.02%     
==========================================
  Files        1142     1144       +2     
  Lines       57448    57506      +58     
  Branches     8235     8243       +8     
==========================================
+ Hits        41443    41497      +54     
- Misses      14706    14708       +2     
- Partials     1299     1301       +2

Flag	Coverage Δ
#smoketests	72.16% <93.1%> (+0.02%)	⬆️
#unittests	69.78% <93.1%> (+0.02%)	⬆️

Impacted Files	Coverage Δ
nipype/interfaces/afni/__init__.py	100% <ø> (ø)	⬆️
nipype/interfaces/afni/utils.py	79.55% <100%> (+1.65%)	⬆️
.../interfaces/afni/tests/test_auto_QwarpPlusMinus.py	85.71% <85.71%> (ø)
nipype/interfaces/afni/tests/test_auto_Unifize.py	85.71% <85.71%> (ø)

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[satra]

@emdupre - could you please merge current master, resolve conflicts, and push again?