[REF] Rename kernel_estimator attribute to kernel_transformer

[tsalo]

Closes None. References #195. Pending #163.

Changes proposed in this pull request:

• Change CBMAEstimators' kernel_estimator attribute to kernel_transformer.

[codecov]

Codecov Report

Merging #197 into master will not change coverage.
The diff coverage is 80%.

@@          Coverage Diff           @@
##           master    #197   +/-   ##
======================================
  Coverage    53.2%   53.2%           
======================================
  Files          71      71           
  Lines        4368    4368           
======================================
  Hits         2324    2324           
  Misses       2044    2044

Impacted Files	Coverage Δ
nimare/parcellate/mamp.py	0% <0%> (ø)	⬆️
nimare/meta/cbma/ale.py	93.06% <84.61%> (ø)	⬆️
nimare/meta/cbma/mkda.py	90.55% <85%> (ø)	⬆️

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[tsalo]

@tyarkoni I know that the plan was to wait until #163 was merged, but I imagine that the PyMARE integration will actually take a while. Do you mind if I merge this now? I doubt it will cause major conflicts for your branch.

[tyarkoni]

Go for it!