[ENH] OWEditDomain: Data info displayed in the status bar

[aturanjanin]

Description of changes

Input/output data info displayed in the status bar.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #4456 into master will decrease coverage by 4.32%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4456      +/-   ##
==========================================
- Coverage   87.46%   83.13%   -4.33%     
==========================================
  Files         405      268     -137     
  Lines       74128    53932   -20196     
==========================================
- Hits        64836    44837   -19999     
+ Misses       9292     9095     -197     

[VesnaT]

If one creates duplicated variable names, there is nothing on the output, but the info summary remains unchanged.
To reproduce: File (Iris) -> Edit Domain (in the Name line edit replace sepal length with sepal width and click apply)