Check checksum for plugin downloads

* Compare the MD5 checksum when downloading plugins
* Reduced log spam due to http requests
* Removed 'GetTempFileResponse' function from HttpClientManager
* Fixed caching for HttpClientManager

MediaBrowser.Model/Updates/InstallationInfo.cs

@@ -36,11 +36,5 @@ namespace MediaBrowser.Model.Updates
         /// </summary>
         /// <value>The update class.</value>
         public PackageVersionClass UpdateClass { get; set; }
-
-        /// <summary>
-        /// Gets or sets the percent complete.
-        /// </summary>
-        /// <value>The percent complete.</value>
-        public double? PercentComplete { get; set; }
     }
 }