Random data: Add output summary, fix adding variables on keydown on combo

[janezd]

Issue

Fixes #97.

Description of changes

1. Combo value was changed when the down key was pressed, and the currentTextChanged triggers adding a variables. This has been resolved by setting the focus policy to none.
2. Output summary is added and tested.

Includes

• [X] Code changes
• [X] Tests

[codecov-io]

Codecov Report

Merging #98 (7e1e2cf) into master (17d6b96) will decrease coverage by 0.00%. The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master      #98      +/-   ##
==========================================
- Coverage   87.88%   87.88%   -0.01%     
==========================================
  Files          19       19              
  Lines        2667     2675       +8     
  Branches      314      315       +1     
==========================================
+ Hits         2344     2351       +7     
- Misses        293      294       +1     
  Partials       30       30              

Impacted Files	Coverage Δ
orangecontrib/educational/widgets/owrandomdata.py	97.81% <88.88%> (-0.27%)	:arrow_down:

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[ajdapretnar]

This works well for the output summary. But the first issue is still present. I think it is my fault for not describing the bug well enough. So adding a variable happens only when hovering over the comboBox.