FIX-#419: Handle incompatibility issues between timedelta64 dtypes with Altair

[cgarciae]

Overview

Fixes #419 by handling timedelta64 columns in sanitize_dataframe.

Changes

• Adds tests for the timedelta64 and interval dtypes.
• Converts timedelta64 columns to dt.seconds inside the sanitize_dataframe function.

[codecov]

Codecov Report

Merging #444 (2f58d94) into master (4c95211) will decrease coverage by 0.02%.
The diff coverage is 78.26%.

@@            Coverage Diff             @@
##           master     #444      +/-   ##
==========================================
- Coverage   65.63%   65.60%   -0.03%     
==========================================
  Files          55       55              
  Lines        4423     4440      +17     
==========================================
+ Hits         2903     2913      +10     
- Misses       1520     1527       +7     

Impacted Files	Coverage Δ
lux/executor/PandasExecutor.py	89.09% <57.14%> (-0.76%)	⬇️
lux/vislib/altair/AltairChart.py	84.61% <85.71%> (-0.64%)	⬇️
lux/utils/date_utils.py	90.24% <88.88%> (-0.67%)	⬇️
lux/vislib/altair/Heatmap.py	93.10% <0.00%> (-3.45%)	⬇️
lux/vislib/altair/ScatterChart.py	93.93% <0.00%> (-3.04%)	⬇️

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[dorisjlee]

This looks good, can we indicate on the visualization labels that the attribute is now "attr [secs]"?

[cgarciae]

@dorisjlee what is the best way to do this? Is it just changing the column name or something more fancy?

[dorisjlee]

We can do this the same way we set an axis title like we do for the Histogram "axis_name (binned)" for Altair and Matplotlib (see example source).