[ENH] Color widget: Add reset button

[janezd]

Issue

Fixes #4665.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #4718 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           master    #4718    +/-   ##
========================================
  Coverage   83.69%   83.70%            
========================================
  Files         280      275     -5     
  Lines       56420    55626   -794     
========================================
- Hits        47223    46563   -660     
+ Misses       9197     9063   -134     

[ajdapretnar]

This works well, just the button is fairly small compared to the widget.

[janezd]

Indeed it is, but Reset button is supposed to be small. :)
(It's also easier to implement it this way.)