Added Disk space information to system.

(cherry picked from commit 91625019378247b1c6ab85afaee23f2855e3298b)

src/NzbDrone.Api/DiskSpace/DiskSpaceResource.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NzbDrone.Api.REST;
+
+namespace NzbDrone.Api.DiskSpace
+{
+    public class DiskSpaceResource : RestResource
+    {
+        public string DriveLetter { get; set; }
+        public string FreeSpace { get; set; }
+        public string TotalSpace { get; set; }
+    }
+}