feat(eda): added density parameter to plot_diff(df)

[devinllu]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes Issue #683

• Added density parameter to plot_diff(df)
• Refactored some existed functions such as kde_viz()
• Displays density histograms when proper config object is passed in (Ex: {diff.density: True})

How Has This Been Tested?

Manually tested via Jupyter Notebook

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Snapshot of tests included below

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Checklist:

• My code follows the style guidelines of this project
• I have already squashed the commits and make the commit message conform to the project standard.
• I have already marked the commit with "BREAKING CHANGE" or "Fixes #" if needed.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[jinglinpeng]

I find the code of kde_viz_panel is almost same as kde_viz_figure. Could we just call kde_viz_figure in kde_viz_panel? E.g.,

fig = kde_viz_figure(...)
return panel(fig)...

[devinllu]

Normally I would've just made both of these into 1 function, however if you look at the return types they're both different (one specifically returns Panel, the other Figure). That's why I wrote 2 different functions. Thoughts?

[jinglinpeng]

In the kde_viz_panel function, you could first get fig using kde_viz_figure function, then warp it to the Panel type and return. In this way the code of generating fig part is not redundant.

[devinllu]

@jinglinpeng

[devinllu]

Ah I see what you're saying I misread it

[jinglinpeng]

Hi @devinllu , good job! I think we can merge the PR after you rebase and fix my last comment.