add WINIX_PLUGIN_QUIT and WINIX_QUIT plugins messages

While here:
- rename WINIX_CLOSE to WINIX_PREPARE_TO_CLOSE

winixd/core/app.cpp

@@ -408,7 +408,7 @@ void App::Close()
 	{
 		Winix::Lock lock(synchro);
 
-		plugin.Call((Winix::Session*)0, WINIX_CLOSE);
+		plugin.Call((Winix::Session*)0, WINIX_PREPARE_TO_CLOSE);
 
 		session_manager.SaveSessions();
 		session_manager.DeleteSessions();
@@ -421,6 +421,17 @@ void App::Close()
 
 	WaitForThreads();
 	// now all others threads are terminated
+
+	/*
+	 * at the moment plugins are removed when winix is finishing
+	 * but in the future we can add plug-in removal before the end
+	 */
+	plugin.Call(nullptr, WINIX_PLUGIN_QUIT);
+
+	/*
+	 * this is the last message for plugins
+	 */
+	plugin.Call(nullptr, WINIX_QUIT);
 }