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/Converters/LauncherPageConverters.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+
+using Avalonia.Collections;
+using Avalonia.Data.Converters;
+
+namespace SourceGit.Converters
+{
+    public static class LauncherPageConverters
+    {
+        public static readonly FuncMultiValueConverter<object, bool> ToTabSeperatorVisible =
+            new FuncMultiValueConverter<object, bool>(v =>
+            {
+                if (v == null)
+                    return false;
+
+                var array = new List<object>();
+                array.AddRange(v);
+                if (array.Count != 3)
+                    return false;
+
+                var self = array[0] as ViewModels.LauncherPage;
+                if (self == null)
+                    return false;
+
+                var selected = array[1] as ViewModels.LauncherPage;
+                var collections = array[2] as AvaloniaList<ViewModels.LauncherPage>;
+
+                if (selected != null && collections != null && (self == selected || collections.IndexOf(self) + 1 == collections.IndexOf(selected)))
+                {
+                    return false;
+                }
+                else
+                {
+                    return true;
+                }
+            });
+    }
+}