[MacOS] added menu bar items for Copy, Cut, Paste, Select All

[veler]

Pull request type

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• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
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What is the current behavior?

Issue Number: #1203

What is the new behavior?

After investigation, I found that the ultimate problem is that the app lack of a menu bar with keyboard shortcut associated to commands like Cut, Copy, Paste and Select All. I added these menus and made them doing a copy/paste/cut/select all in the element that has the focus.

Other information

Quality check

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• Did you follow the code style guideline as described in CONTRIBUTING.md
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• If necessary and if possible, did you verify your changes on:
  • Windows
  • macOS
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