Clean up some objects from windowWillClose: rather than dealloc, so we don't need to ensure the main thread
Clean up some objects from windowWillClose: rather than dealloc, so we don't need to ensure the main thread

JackieXie168/skim,JackieXie168/skim,JackieXie168/skim,JackieXie168/skim,JackieXie168/skim