Add user actions to make more easy access to design files

[volodymyrkochyn]

Motivate of the pull request

• To address an existing issue. If so, please provide a link to the issue:
• Breaking new feature. If so, please describe details in the description part.

Describe the technical details

Make access to the design files settings fester.

Which part of the code base require a change

• Library: projnavigator, foedagcore
• Plug-in:
• Engine
• Documentation
• Regression tests
• Continous Integration (CI) scripts

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 38 lines in your changes missing coverage. Please review.

Project coverage is 14.62%. Comparing base (5c5f050) to head (00df579).

Files	Patch %	Lines
src/ProjNavigator/sources_form.cpp	0.00%	27 Missing ⚠️
src/MainWindow/main_window.cpp	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1655      +/-   ##
==========================================
- Coverage   14.62%   14.62%   -0.01%     
==========================================
  Files         477      477              
  Lines       63521    63548      +27     
  Branches    25932    25875      -57     
==========================================
  Hits         9291     9291              
- Misses      53042    53055      +13     
- Partials     1188     1202      +14     

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