Fix transparency issues on Windows 10

[OlegTopalov]

Issue: closes #1405

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.

• issue was opened to discuss proposed changes before starting implementation. It is important do discuss changes before implementing them (Why should we add it? How should it work? How should it look? Where will it be? ...).
• during development, node version specified in package.json was used (ie using nvm).
• package versions and package-lock.json were not changed (npm install --no-save).
• app version number was not changed.
• all new code has tests to ensure against regressions.
• npm run lint reports no offenses.
• npm run test is error-free.
• README and CHANGELOG were updated accordingly.
• after PR is approved, all commits in it are squashed

Description of the Change

Verification Process

Based on that issue in Electron: electron/electron#8847
I was able to fix the issue by setting the transparency to True always and HasShadow = false.
However, since the application has a transparency setting, I've updated the method to calculate the background color to check for the transparency setting. Note, that it was tested only on Win10

Other information

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fa317a2) 72.39% compared to head (7311102) 72.39%.
Report is 4 commits behind head on trunk.

Additional details and impacted files

@@           Coverage Diff           @@
##            trunk    #1412   +/-   ##
=======================================
  Coverage   72.39%   72.39%           
=======================================
  Files          14       14           
  Lines         355      355           
=======================================
  Hits          257      257           
  Misses         98       98           

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[hovancik]

Hi and thanks, just checked on Linux and mac and seems Ok. Could you please add to changelog sth like

### Fixed
- transparency issues on Windows 10

[OlegTopalov]

Hi and thanks, just checked on Linux and mac and seems Ok. Could you please add to changelog sth like

### Fixed
- transparency issues on Windows 10

updated