Refactor LuxGroupBy using multiple inheritance

[westernguy2]

Overview

Refactored LuxGroupBy to look similar to how Pandas structures GroupBy objects, separating them in LuxDataFrameGroupBy and LuxSeriesGroupBy. This will allow us to extend methods for specific types of GroupBy objects.

Also fixed a minor bug for testing purposes.

Changes

Used multiple inheritance to ensure each LuxGroupBy child class also inherits the corresponding Pandas version. They all have a parent class of LuxGroupBy. Also fixed a bug where the Pandas tests were not using Lux since it was using a different type of Series object. This was added to __init__.py to ensure it points to LuxSeries.

Example Output

No example output for this PR.

[codecov]

Codecov Report

Merging #309 (cf26ab3) into master (4de06dc) will decrease coverage by 0.10%.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master     #309      +/-   ##
==========================================
- Coverage   81.08%   80.97%   -0.11%     
==========================================
  Files          50       50              
  Lines        3569     3596      +27     
==========================================
+ Hits         2894     2912      +18     
- Misses        675      684       +9     

Impacted Files	Coverage Δ
lux/core/series.py	87.61% <92.85%> (+0.80%)	⬆️
lux/core/groupby.py	83.60% <95.23%> (-6.19%)	⬇️
lux/core/__init__.py	86.66% <100.00%> (+0.95%)	⬆️
lux/vislib/altair/Heatmap.py	93.10% <0.00%> (-3.45%)	⬇️
lux/vislib/matplotlib/Heatmap.py	96.66% <0.00%> (-1.67%)	⬇️
lux/vislib/matplotlib/ScatterChart.py	78.78% <0.00%> (-1.52%)	⬇️
lux/vislib/altair/Histogram.py	89.58% <0.00%> (ø)

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[dorisjlee]

Thanks @westernguy2! If I understand this correctly, we don't currently support series groupby (only LuxDataFrameGroupBy) but with this new change, we can now expect Lux to work with the case of series groupby? If this is the case, could you point to the specific test either on the Pandas test suite, or adding our own tests to check that series groupby is working as intended?

[westernguy2]

The SeriesGroupBy test that was failing was actually not fixed by this new implementation. However, while debugging that issue, I tried this new format for LuxGroupBy that seemed to be better than the old format.

I can add a test similar to the ones related to SeriesGroupBy that were failing, later tonight!

[westernguy2]

Also, yes, this PR also allows metadata propagation through SeriesGroupBy which is not supported currently, I had forgotten about that! I will add some tests for this new feature.

[dorisjlee]

That's great, I was thinking that this new SeriesGroupBy seems to better support the metadata propagation. I'll wait for the tests before merging this in.

[westernguy2]

@dorisjlee Added a test for SeriesGroupBy!

[dorisjlee]

Thanks @westernguy2, this looks good! Merging this in now!