Fix KElbow get_params

[bbengfort]

This PR fixes #1232 which reported a bug that caused a problem to occur when users call KElbow.get_params(), e.g. in a notebook when they want to render the scikit-learn rich visualization of the estimator.

I have made the following changes:

1. Updated KElbow to ensure it stores all hyperparams and only creates learned params in fit()
2. Added tests to ensure get_params works for KElbow
3. Updated the wrapper to prevent infinite recursion and give a more meaningful attribute error for future debugging

Sample Code and Plot

from sklearn.cluster import KMeans
from yellowbrick.cluster import KElbowVisualizer
visualizer = KElbowVisualizer(KMeans(), k=(2,12))
visualizer.get_params()

The above code snippet should not produce an exception: AttributeError: 'KMeans' object has no attribute 'k'

Questions for the @DistrictDataLabs/team-oz-maintainers:

• [x] Should we add a test for get_params for all our models to make sure this doesn't happen?
• [x] @lwgray this is related to an issue we were experiencing in notebooks before; where the exception happened if the visualizer was the last line in the cell and scikit-learn was trying to render it; do you remember what Visualizer that was?

CHECKLIST

• [x] Is the commit message formatted correctly?
• [ ] ~Have you noted the new functionality/bugfix in the release notes of the next release?~

• [ ] ~Included a sample plot to visually illustrate your changes?~
• [x] Do all of your functions and methods have docstrings?
• [x] Have you added/updated unit tests where appropriate?
• [ ] ~Have you updated the baseline images if necessary?~
• [x] Have you run the unit tests using pytest?
• [x] Is your code style correct (are you using PEP8, pyflakes)?
• [ ] ~Have you documented your new feature/functionality in the docs?~

• [ ] ~Have you built the docs using make html?~

[codecov[bot]]

Codecov Report

Merging #1251 (941e793) into develop (233d9d1) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1251   +/-   ##
========================================
  Coverage    90.57%   90.58%           
========================================
  Files           92       92           
  Lines         5209     5213    +4     
========================================
+ Hits          4718     4722    +4     
  Misses         491      491           

Impacted Files	Coverage Δ
yellowbrick/model_selection/dropping_curve.py	92.18% <ø> (ø)
yellowbrick/cluster/elbow.py	97.81% <100.00%> (-0.04%)	:arrow_down:
yellowbrick/utils/wrapper.py	100.00% <100.00%> (ø)

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[lwgray]

It was dropping curve...

[lwgray]

@bbengfort You should open an issue to create get_params test.

[bbengfort]

I just checked DroppingCurve - get_params works fine, so I guess you fixed it.

[bbengfort]

@lwgray Issue #1252 opened at your request.

[bbengfort]

I also added a test for DroppingCurve.get_params.