Mixins for storing recent files in QSettings

[janezd]

Issue

Ref biolab/orange3#4919.

Description of changes

Includes

• Code changes
• Tests
• Documentation

[codecov-commenter]

Codecov Report

❌ Patch coverage is 38.58268% with 78 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.71%. Comparing base (cbf5b10) to head (0a27ec5).

Files with missing lines	Patch %	Lines
orangewidget/utils/filedialogs.py	38.58%	78 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #291      +/-   ##
==========================================
- Coverage   72.07%   71.71%   -0.37%     
==========================================
  Files          34       34              
  Lines        9126     9229     +103     
==========================================
+ Hits         6578     6619      +41     
- Misses       2548     2610      +62     

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