[FIX] Scatter Plot: update class density

[jerneju]

Issue

Enable/disable class density on changes to color variable.

Description of changes

Includes

• Code changes
• Tests
• Documentation

[codecov-io]

Codecov Report

Merging #2238 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2238      +/-   ##
==========================================
+ Coverage   67.64%   67.65%   +<.01%     
==========================================
  Files         319      319              
  Lines       54871    54871              
==========================================
+ Hits        37119    37121       +2     
+ Misses      17752    17750       -2

---

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 6f2ae63...f1c73fe. Read the comment docs.