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.Controller/Session/ISessionManager.cs

@@ -171,6 +171,16 @@ namespace MediaBrowser.Controller.Session
         /// <returns>Task.</returns>
         Task SendPlaystateCommand(string controllingSessionId, string sessionId, PlaystateRequest command, CancellationToken cancellationToken);
 
+        /// <summary>
+        /// Sends the message to admin sessions.
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="name">The name.</param>
+        /// <param name="data">The data.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        /// <returns>Task.</returns>
+        Task SendMessageToAdminSessions<T>(string name, T data, CancellationToken cancellationToken);
+
         /// <summary>
         /// Sends the message to user sessions.
         /// </summary>