* replace the `YEAR` tab with `OVERVIEW` tab, which will analyze most recent 20K commits
* use `LiveChartsCore.SkiaSharpView.Avalonia` instead of a custom chart view
* move resources and styles for macOS caption button to `CaptionButtonsMacOS` because it is never used by others and should not been changed
* add `IsCloseButtonOnly` property to `CaptionButtons` and `CaptionButtonsMacOS` and replace the controls in windows
* input font name directly instead of a font picker because localized font family name is not supported by Avalonia
* fallback monospace font to default font
* remove unused code
* remove dotnet-tool.json because the project does not rely on any dotnet tools.
* remove Directory.Build.props because the solution has only one project.
* move src/SourceGit to src. It's not needed to put all sources into a subfolder of src since there's only one project.
