Add preview for Table signal

[janezd]

Issue

Ref: #5873

Based on https://github.com/biolab/orange-widget-base/pull/198.

Description of changes

Add previewer for Table.

We probably want to add one for Distance Matrix, and that would be it (for signals in core widgets), I guess.

Includes

• [X] Code changes
• [ ] Tests
• [ ] Documentation

[codecov[bot]]

Codecov Report

Merging #5956 (f8a2076) into master (258b49b) will decrease coverage by 0.00%. The diff coverage is 50.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5956      +/-   ##
==========================================
- Coverage   86.46%   86.46%   -0.01%     
==========================================
  Files         315      315              
  Lines       67667    67673       +6     
==========================================
+ Hits        58508    58512       +4     
- Misses       9159     9161       +2