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/Commands/Apply.cs

@@ -0,0 +1,19 @@
+namespace SourceGit.Commands
+{
+    public class Apply : Command
+    {
+        public Apply(string repo, string file, bool ignoreWhitespace, string whitespaceMode, string extra)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = "apply ";
+            if (ignoreWhitespace)
+                Args += "--ignore-whitespace ";
+            else
+                Args += $"--whitespace={whitespaceMode} ";
+            if (!string.IsNullOrEmpty(extra))
+                Args += $"{extra} ";
+            Args += $"\"{file}\"";
+        }
+    }
+}