[ENH] Add Text2Vest and Vest2Text interfaces

[jdkent]

Summary

Create Text2Vest Interface to work directly with FILMGLS

References poldracklab/fitlins#114

List of changes proposed in this PR (pull-request)

• add Text2Vest interface
• add Vest2Text interface

[codecov]

Codecov Report

Merging #3447 (62d8c46) into master (f8f7fb5) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3447      +/-   ##
==========================================
+ Coverage   65.23%   65.24%   +0.01%     
==========================================
  Files         308      308              
  Lines       40625    40643      +18     
  Branches     5361     5361              
==========================================
+ Hits        26500    26518      +18     
  Misses      13049    13049              
  Partials     1076     1076              

Flag	Coverage Δ
unittests	64.97% <100.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
nipype/interfaces/fsl/__init__.py	100.00% <ø> (ø)
nipype/interfaces/fsl/utils.py	64.46% <100.00%> (+0.69%)	⬆️

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[effigies]

Overall LGTM. Some minor suggestions.

[effigies]

Thanks!