Maya: AssetManager: 1. Added asset_manager_dock_widget.py to subclass QDockWidget. Startup procedure for AssetManager checks now against type of dock widget and not against name aymore. 2. Cleaned closeEvents for AssetManager and AssetManagerDockWidget. Introduced stop_all_threads_and_timer() method on AssetManager, that is ment to stop all timer, threads and processes initiated on AssetManager startup when closing.