Cleaned up all .csproj files.

Moved things around to make cleaner build files.
Implementing everything with `netstandard2.1` and then thin wrapper executables using .net5

Executables/net5/Duplicati.CommandLine.RecoveryTool/Program.cs

@@ -0,0 +1,9 @@
+namespace Duplicati.CommandLine.RecoveryTool.Net5
+{
+    // Wrapper class to keep code independent
+    public static class Program
+    {
+        public static int Main(string[] args)
+            => Duplicati.CommandLine.RecoveryTool.Program.Main(args);
+    }
+}