FIX: Multi-step-reg / composite transform misformation

[mgxd]

Hopefully the end of this mini-saga - thanks to @tsalo @mattcieslak for taking a look.

Changes included in this:

• Fix ordering in multi-step-reg's anat2std_xfm and std2anat_xfm
• Disassemble transform components in standalone nodes for improved transparency
• Change inputnode fields to reflect intermediate are being used.
• Cache intermediate <-> std transforms to node working directories.
• Add SimpleITK as a dependency for assembling inverse std2anat xfm, until ants CompositeTransformUtil is addressed.

[tsalo]

Just one idea for a docstring and one question, really

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 0.37%. Comparing base (e5ed154) to head (29c87b6).
Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
nibabies/workflows/base.py	0.00%	3 Missing ⚠️
nibabies/interfaces/patches.py	0.00%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (e5ed154) and HEAD (29c87b6). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (e5ed154)	HEAD (29c87b6)
	7	4

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #433       +/-   ##
==========================================
- Coverage   56.12%   0.37%   -55.75%     
==========================================
  Files          70      69        -1     
  Lines        6697    6581      -116     
  Branches      834     821       -13     
==========================================
- Hits         3759      25     -3734     
- Misses       2734    6556     +3822     
+ Partials      204       0      -204     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.