Replace relative imports with absolute ones

[tsalo]

Closes None. Absolute imports are recommended by PEP8, and I think this will make it easier to identify any circular import problems as we start reorganizing base classes.

[codecov]

Codecov Report

Merging #674 (0d97212) into main (b806510) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #674   +/-   ##
=======================================
  Coverage   85.28%   85.28%           
=======================================
  Files          40       40           
  Lines        4513     4513           
=======================================
  Hits         3849     3849           
  Misses        664      664           

Impacted Files	Coverage Δ
nimare/annotate/cogat.py	91.35% <100.00%> (ø)
nimare/annotate/gclda.py	97.35% <100.00%> (ø)
nimare/annotate/text.py	90.32% <100.00%> (ø)
nimare/base.py	88.49% <100.00%> (ø)
nimare/correct.py	93.06% <100.00%> (ø)
nimare/dataset.py	89.72% <100.00%> (ø)
nimare/decode/continuous.py	94.73% <100.00%> (ø)
nimare/decode/discrete.py	96.61% <100.00%> (ø)
nimare/decode/encode.py	85.18% <100.00%> (ø)
nimare/extract/extract.py	42.97% <100.00%> (ø)
... and 17 more

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[tsalo]

@jdkent @adelavega @JulioAPeraza do any of you have any issues with me merging this?

[jdkent]

LGTM, I do not think any of the import statements are overly verbose written out explicitly
relevant PEP8 section

[adelavega]

Fine w/ me

[JulioAPeraza]

Fine with me too.