appearance - show keyboard hints

[iksi4prs]

Motivation
Improve usability by showing user keyboard shortcuts on screen

Scope
Added new tab called "Appearance" under settings.
(Name and icon were selected to be same as in Google chrome).
The new tab has a checkbox to control whether keyboard hints should be visible in top bar.
For backwards compatibility, the checkbox controls visibility of hints only on top bar, not on bottom (eg F4, F5, etc)
See attached image.
(Future feature in settings is to move also "Theme" from "General" to "Appearance", same as in Google Chrome)

[codecov-commenter]

Codecov Report

Attention: 22 lines in your changes are missing coverage. Please review.

Comparison is base (3330b67) 92.89% compared to head (d02b53c) 92.50%.

Files	Patch %	Lines
...mentations/Settings/AppearanceSettingsViewModel.cs	25.00%	12 Missing ⚠️
src/Camelot.Services/AppearanceSettingsService.cs	55.00%	8 Missing and 1 partial ⚠️
...ns/MainWindow/Operations/TopOperationsViewModel.cs	75.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #67      +/-   ##
==========================================
- Coverage   92.89%   92.50%   -0.39%     
==========================================
  Files         185      187       +2     
  Lines        4830     4873      +43     
  Branches      388      392       +4     
==========================================
+ Hits         4487     4508      +21     
- Misses        288      309      +21     
- Partials       55       56       +1     

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