[FIX] ROC shows all points, including the last

[janezd]

Description of changes

• Fixes Error in ROC Analysis plot #5119: The last point on the curve was not shown.
• Fixes the threshold shown at the bottom-left point (now set to 1; used to be 1 + the highest p in the data)
• Adds simpler preview data
• Shows ticks for actual FPR/TPR values, if there are <15 unique values

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #5138 (1eca4d6) into master (c2812c5) will increase coverage by 0.00%.
The diff coverage is 96.00%.

@@           Coverage Diff           @@
##           master    #5138   +/-   ##
=======================================
  Coverage   84.77%   84.77%           
=======================================
  Files         286      286           
  Lines       60084    60099   +15     
=======================================
+ Hits        50936    50949   +13     
- Misses       9148     9150    +2     

[janezd]

@BlazZupan, do you like the changed ticks when the data is small (to be used in particular for teaching)? If you do, you can review and merge if you will. (The failing check is irrelevant.) If not, say so and I'll remove the commit.

[BlazZupan]

I have tested this widget on several smaller test sets, where I could draw the ROC curve manually. Now it works fine, and the error was corrected. I also like the changes with the ticks.