Auto-Organize: Async operation and instant feedback UI (reworked)

This commit includes changes to enable and stabilize asyncronous
operation in the auto-organize area. Here are the key points:

- The auto-organize correction dialog is now closed (almost) instantly.
This means that the user does not have to wait until the file copy/move
operation is completed in order to continue. (even with local HDs the
copy/move process can take several minutes or even much longer with
network destination).
- This commit also implements locking of files to be organized in order
to prevent parallel processing of the same item. In effect, there can be
2 or more manual organization operations active even while the normal
auto-organization task is running without causing any problems
- The items that are currently being processed are indicated as such in
the log with an orange color and a spinner graphic
- The client display is refreshed through websocket messages
- A side effect of this is that other clients showing the auto-organize
log at the same time are always up-to-date as well

MediaBrowser.Model/FileOrganization/FileOrganizationResult.cs

@@ -95,6 +95,12 @@ namespace MediaBrowser.Model.FileOrganization
         /// <value>The size of the file.</value>
         public long FileSize { get; set; }
 
+        /// <summary>
+        /// Indicates if the item is currently being processed.
+        /// </summary>
+        /// <remarks>Runtime property not persisted to the store.</remarks>
+        public bool IsInProgress { get; set; }
+
         public FileOrganizationResult()
         {
             DuplicatePaths = new List<string>();