ENH: Add visualization of head motion correction

[mnoergaard]

This PR addresses issue #169 by implementing a visualization of the head motion correction, similarly as produced by petprep_hmc. This allows the user to visually inspect the data before and after motion, and is a nice addition to the carpet plot visualization above showing the DVARS and framewise displacement.

[codecov]

Codecov Report

❌ Patch coverage is 95.63319% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.23%. Comparing base (b76cd74) to head (217772b).
⚠️ Report is 38 commits behind head on main.

Files with missing lines	Patch %	Lines
petprep/interfaces/motion.py	95.27%	3 Missing and 4 partials ⚠️
petprep/workflows/pet/base.py	66.66%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #171      +/-   ##
==========================================
+ Coverage   79.66%   80.23%   +0.57%     
==========================================
  Files          82       84       +2     
  Lines        6138     6366     +228     
  Branches      618      638      +20     
==========================================
+ Hits         4890     5108     +218     
- Misses       1092     1096       +4     
- Partials      156      162       +6     

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[mnoergaard]

Think I am quite happy with the state of this now - @mathesong WDYT?

You can patch in the code from this PR when running PETPrep with Docker using
--patch petprep=/github_path/petprep/petprep

[mathesong]

This looks awesome!! This is just what we've been missing. And I really like the markers of the larger overall displacement too! I've just been running PETPrep on a large dataset for the last two days, so maybe I'll run it again over the weekend to get the snazzy new motion plots.