[ENH] Feature Statistics: Add median

[janezd]

Issue

Resolves #5317.

Description of changes

• Add a column with median
• Show the most frequent value of discrete values in column with medians rather than with means,
• Rename column "Center" to "Mean"

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #5325 (395f2e4) into master (69e580d) will decrease coverage by 0.01%.
The diff coverage is 54.54%.

@@            Coverage Diff             @@
##           master    #5325      +/-   ##
==========================================
- Coverage   85.35%   85.34%   -0.02%     
==========================================
  Files         301      301              
  Lines       62035    62043       +8     
==========================================
- Hits        52950    52948       -2     
- Misses       9085     9095      +10     

[janezd]

That's it - tests don't cover sorting, but that's also the case for most other scores, and there's also not much to test, so I won't add them.

[irgolic]

This is cool. I think mean/median is much more transparent and easy to understand than center.

Sidenote:

Dispersion is confusing too, similarly as center was. I had to open the documentation to understand what the values meant. This information could easily be in a tooltip when hovering over the column/column header. Also, the docs show a really old screenshot, which still has a controlArea/mainArea split. Having docs is great, but having out-of-date docs is not. However, keeping them up-to-date by hand is a three-man full-time-job. Let's talk about this over tea.