Allow different sorters to work with Vis Object

[jinimukh]

Overview

This PR introduces a way to incorporate different sorters for Vis Objects. Currently, this only includes interestingness and alphabetical sorts, but later on, we can extend this class.

Changes

-- add sorters.py in utils -- add lux.config.sorter in config -- add tests in test_config

Example Output

TBD

[codecov[bot]]

Codecov Report

Merging #350 (d08c17c) into master (623e5f3) will increase coverage by 0.30%. The diff coverage is 91.42%.

@@            Coverage Diff             @@
##           master     #350      +/-   ##
==========================================
+ Coverage   65.94%   66.24%   +0.30%     
==========================================
  Files          55       56       +1     
  Lines        4416     4468      +52     
==========================================
+ Hits         2912     2960      +48     
- Misses       1504     1508       +4     

Impacted Files	Coverage Δ
lux/utils/orderings.py	84.61% <84.61%> (ø)
lux/_config/config.py	77.27% <100.00%> (+1.72%)	:arrow_up:
lux/action/correlation.py	86.66% <100.00%> (ø)
lux/action/enhance.py	100.00% <100.00%> (ø)
lux/action/filter.py	91.66% <100.00%> (ø)
lux/action/temporal.py	96.61% <100.00%> (ø)
lux/action/univariate.py	89.13% <100.00%> (ø)
lux/vis/VisList.py	51.04% <100.00%> (-0.26%)	:arrow_down:
lux/vislib/altair/ScatterChart.py	96.96% <0.00%> (+3.03%)	:arrow_up:
... and 1 more

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