[ticket/14462] Further speed improvements

- Cache the secondary container
- Only initialize tasks/modules that are being used
- Add timeout error message in the AJAX UI

PHPBB3-14462

phpBB/phpbb/install/module/update_filesystem/task/download_updated_files.php

@@ -101,7 +101,6 @@ class download_updated_files extends task_base
 				),
 			));
 
-			$this->iohandler->send_response();
 			throw new user_interaction_required_exception();
 		}
 	}

phpBB/phpbb/install/module/update_filesystem/task/show_file_status.php

@@ -136,7 +136,6 @@ class show_file_status extends task_base
 			));
 
 			// Show results to the user
-			$this->iohandler->send_response();
 			throw new user_interaction_required_exception();
 		}
 		else