Replace deprecated "_phase" suffix in reproin heuristic with "part-phase" entity

[tsalo]

Closes #769. This is working on DICOMs associated with https://openneuro.org/datasets/ds005250.

Changes proposed:

• Track previous and next sequence info in ReproIn's infotodict.
• Rename s variable to curr_seqinfo for improved clarity. Moved to #779.
• For non-SBRef, non-fieldmap scans, set "part" entity to "phase" for phase data instead of setting the suffix to "phase".
• For magnitude non-SBRef, non-fieldmap scans, check if the next sequence has the same series_description and is a phase scan. If it is, set "part" to "mag".

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.15%. Comparing base (a0a3635) to head (59bb2ec). Report is 16 commits behind head on master.

Files with missing lines	Patch %	Lines
heudiconv/heuristics/reproin.py	90.90%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #770 +/- ## ========================================== + Coverage 82.08% 82.15% +0.06% ========================================== Files 42 42 Lines 4215 4230 +15 ========================================== + Hits 3460 3475 +15 Misses 755 755 ```

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[yarikoptic]

Rename s variable to curr_seqinfo for improved clarity.

yeah, but complicates review a little due to diff now including changes I can ignore or not and need to decide when looking...

Could you submit a separate PR with that typo fix and such a rename (so no functionality change) and then let's improve this one -- yet to grasp on all the changes, and as we do not have any nice testing for reproin heuristic, I wonder how we could add one :-/ I would really be shy to accept without some way to test. Locally I could do using smth like https://github.com/nipy/heudiconv/blob/master/utils/test-compare-two-versions.sh but could we do better?!

[tsalo]

:+1: I've opened #779 with the variable name change.

[yarikoptic]

@tsalo -- ping on this. Would you happen to get time to address comments?

[tsalo]

Sorry, I've been really busy. I might have time in the next couple of weeks though.