project: reorganize the structure of the project.

* 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.

src/Views/About.axaml

@@ -0,0 +1,103 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:vm="using:SourceGit.ViewModels"
+        xmlns:v="using:SourceGit.Views"
+        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+        x:Class="SourceGit.Views.About"
+        x:DataType="v:About"
+        Icon="/App.ico"
+        Title="{DynamicResource Text.About}"
+        Background="Transparent"
+        SizeToContent="WidthAndHeight"
+        CanResize="False"
+        WindowStartupLocation="CenterScreen"
+        ExtendClientAreaToDecorationsHint="True"
+        ExtendClientAreaChromeHints="NoChrome"
+        SystemDecorations="{OnPlatform Full, Linux=None}">
+  <Grid RowDefinitions="Auto,*" Margin="{OnPlatform 0, Linux=6}">
+    <!-- Custom window shadow for Linux -->
+    <Border Grid.Row="0" Grid.RowSpan="2"
+            Background="{DynamicResource Brush.Window}"
+            Effect="drop-shadow(0 0 6 #A0000000)"
+            IsVisible="{OnPlatform False, Linux=True}"/>
+
+    <!-- TitleBar -->
+    <Grid Grid.Row="0" ColumnDefinitions="Auto,*,Auto" Height="30">
+      <Border Grid.Column="0" Grid.ColumnSpan="3"
+              Background="{DynamicResource Brush.TitleBar}"
+              BorderThickness="0,0,0,1" BorderBrush="{DynamicResource Brush.Border0}"
+              PointerPressed="BeginMoveWindow"/>
+      
+      <Path Grid.Column="0"
+            Width="14" Height="14"
+            Margin="10,0,0,0"
+            Data="{StaticResource Icons.Info}"
+            IsVisible="{OnPlatform True, macOS=False}"/>
+
+      <Grid Grid.Column="0" Classes="caption_button_box" Margin="2,4,0,0" IsVisible="{OnPlatform False, macOS=True}">
+        <Button Classes="caption_button_macos" Click="CloseWindow">
+          <Grid>
+            <Ellipse Fill="{DynamicResource Brush.MacOS.Close}"/>
+            <Path Height="6" Width="6" Stretch="Fill" Fill="#404040" Stroke="#404040" StrokeThickness="1" Data="{StaticResource Icons.Window.Close}"/>
+          </Grid>
+        </Button>
+      </Grid>
+
+      <TextBlock Grid.Column="0" Grid.ColumnSpan="3"
+                 Classes="bold"
+                 Text="{DynamicResource Text.About}"
+                 HorizontalAlignment="Center" VerticalAlignment="Center"
+                 IsHitTestVisible="False"/>
+
+      <Button Grid.Column="2"
+              Classes="caption_button"
+              Click="CloseWindow"
+              IsVisible="{OnPlatform True, macOS=False}">
+        <Path Data="{StaticResource Icons.Window.Close}"/>
+      </Button>
+    </Grid>
+
+    <Grid Grid.Row="1" ColumnDefinitions="Auto,*" Background="{DynamicResource Brush.Window}">
+      <Image Grid.Column="0"
+             Width="200" Height="200"
+             Margin="8,0"
+             Source="/App.ico"
+             HorizontalAlignment="Center"
+             VerticalAlignment="Center"/>
+
+      <StackPanel Grid.Column="1" Orientation="Vertical" Margin="0,8,32,8">        
+        <StackPanel Height="48" Orientation="Horizontal">
+          <TextBlock Classes="bold" Text="SourceGit" FontSize="32" />
+          <Border Margin="12,0,0,0" Height="20" CornerRadius="10" Background="{DynamicResource Brush.Accent1}" Effect="drop-shadow(0 0 6 #40000000)">
+            <TextBlock Classes="monospace" Margin="8,0" Text="{Binding Version}" FontSize="12" Foreground="White"/>
+          </Border>
+        </StackPanel>
+
+        <TextBlock Margin="2,0,0,0" Text="{DynamicResource Text.About.SubTitle}" FontSize="16"/>
+
+        <TextBlock Margin="2,8,0,0" Text="{DynamicResource Text.About.Copyright}" Foreground="{DynamicResource Brush.FG2}"/>
+
+        <StackPanel Orientation="Vertical" Margin="0,24,0,0">
+          <StackPanel Orientation="Horizontal" Height="18">
+            <TextBlock Text="{DynamicResource Text.About.BuildWith}" />
+            <TextBlock Text="Avalonia UI" Cursor="Hand" Foreground="{DynamicResource Brush.Accent1}" TextDecorations="Underline" PointerPressed="OnVisitAvaloniaUI"/>
+            <TextBlock Text=" &amp; " />
+            <TextBlock Text="AvaloniaEdit" Cursor="Hand" Foreground="{DynamicResource Brush.Accent1}" TextDecorations="Underline" PointerPressed="OnVisitAvaloniaEdit"/>
+          </StackPanel>
+
+          <StackPanel Orientation="Horizontal" Height="18" Margin="0,2,0,0">
+            <TextBlock Text="{DynamicResource Text.About.Fonts}" />
+            <TextBlock Text="JetBrains Mono" Cursor="Hand" Foreground="{DynamicResource Brush.Accent1}" TextDecorations="Underline" PointerPressed="OnVisitJetBrainsMonoFont"/>
+          </StackPanel>
+          
+          <StackPanel Orientation="Horizontal" Height="18" Margin="0,2,0,0">
+            <TextBlock Text="{DynamicResource Text.About.SourceCode}" />
+            <TextBlock Text="Github" Cursor="Hand" Foreground="{DynamicResource Brush.Accent1}" TextDecorations="Underline" PointerPressed="OnVisitSourceCode"/>
+          </StackPanel>
+        </StackPanel>
+      </StackPanel>
+    </Grid>
+  </Grid>
+</Window>