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/Models/RevisionFile.cs

@@ -0,0 +1,30 @@
+using Avalonia.Media.Imaging;
+
+namespace SourceGit.Models
+{
+    public class RevisionBinaryFile
+    {
+        public long Size { get; set; } = 0;
+    }
+
+    public class RevisionImageFile
+    {
+        public Bitmap Image { get; set; } = null;
+    }
+
+    public class RevisionTextFile
+    {
+        public string FileName { get; set; }
+        public string Content { get; set; }
+    }
+
+    public class RevisionLFSObject
+    {
+        public LFSObject Object { get; set; }
+    }
+
+    public class RevisionSubmodule
+    {
+        public string SHA { get; set; }
+    }
+}