Added some update APIs to check for updates and download and extract the update package.

Todo: apply updated, UI.

NzbDrone.Core/Model/UpdatePackage.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace NzbDrone.Core.Model
+{
+    public class UpdatePackage
+    {
+        public string Url { get; set; }
+        public string FileName { get; set; }
+        public Version Version { get; set; }
+    }
+}