Improve describe_pipeline by using pipeline's new describe method

[angela97lin]

Still work to be done on this front w/ cross-validation, but grabbing steps from pipeline's describe() rather than automl's clumped parameters for now.

Closes #185, #98

[codecov]

Codecov Report

Merging #190 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #190      +/-   ##
==========================================
+ Coverage   96.78%   96.81%   +0.02%     
==========================================
  Files          91       91              
  Lines        2333     2353      +20     
==========================================
+ Hits         2258     2278      +20     
  Misses         75       75

Impacted Files	Coverage Δ
...components/transformers/imputers/simple_imputer.py	100% <100%> (ø)	⬆️
...l/pipelines/components/transformers/transformer.py	100% <100%> (ø)	⬆️
evalml/model_types/model_types.py	100% <100%> (ø)	⬆️
evalml/utils/logging_utils.py	95.23% <100%> (+0.23%)	⬆️
...lml/tests/pipeline_tests/test_linear_regression.py	100% <100%> (ø)	⬆️
...transformers/feature_selection/feature_selector.py	78.37% <100%> (+4.18%)	⬆️
evalml/models/auto_base.py	93.57% <100%> (-0.2%)	⬇️
evalml/problem_types/problem_types.py	100% <100%> (ø)	⬆️
evalml/pipelines/pipeline_base.py	97.12% <100%> (+0.06%)	⬆️

---

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 247a546...dffa463. Read the comment docs.

[kmax12]

lmk if it'd be helpful to discuss live

[kmax12]

minus my few comments, this looks good. one thing is we probably want to rerun some of the notebooks in the docs to update their output

[angela97lin]

Updated to add number of features (grabbed from estimator) and remove try/except from SimpleImputer.

[kmax12]

everything looks good with the exception of the new warnings that are popping up in the Fraud Prediction Demo

[kmax12]

fixes #98

[kmax12]

Good to merge once tests pass