[FIX] Sort comptable by varex before identifying outlier components

[tsalo]

Closes #176. While this does not clarify everything about this step (e.g., why it is run three times specifically, or why the outlier components are excluded when computing elbows but not when selecting components later), it does resolve the most pressing issue of explaining why the step exists.

This was originally part of #247, but has been split off because it is self-contained and should be merged separately.

Changes proposed in this pull request:

• Sort component table when identifying ncls (components presumably without outlier variance explained) by descending variance explained. Before, the component table was sorted by descending Kappa values when identifying outliers. Per discussions with @handwerkerd, this was identified as a bug.

[tsalo]

#261 was approved by @handwerkerd, so I'm going to merge this once it passes CI.

[jbteves]

LGTM, the sorting is also much more explicit for future reference.

[codecov]

Codecov Report

Merging #295 into master will not change coverage.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master    #295   +/-   ##
======================================
  Coverage    49.1%   49.1%           
======================================
  Files          37      37           
  Lines        2122    2122           
======================================
  Hits         1042    1042           
  Misses       1080    1080

Impacted Files	Coverage Δ
tedana/selection/tedica.py	24.8% <0%> (ø)	⬆️

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[codecov]

Codecov Report

Merging #295 into master will not change coverage.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master    #295   +/-   ##
======================================
  Coverage    49.1%   49.1%           
======================================
  Files          37      37           
  Lines        2122    2122           
======================================
  Hits         1042    1042           
  Misses       1080    1080

Impacted Files	Coverage Δ
tedana/selection/tedica.py	24.8% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 1030a69...6345ecc. Read the comment docs.