[GUI]: stopping the gui should drop subscriptions before stopping the daemon and closing the window

[edouardparis]

From @jp1ac4:

If I close the GUI during IBD of managed bitcoind, there's a warning in the logs: WARN iced_futures::runtime:85: Stream could not run until completion: send failed because receiver is gone. I guess it's fine but perhaps there's a way to close the stream to avoid the warning?

We can have a 2 cycle stop instead of calling State .stop() immediatly on CloseOnRequest message.
first cycle will set stopping = true to the App and makes it stop any subscription by making app.subscription() return Subscription::none() and second cycle can stop the daemon and close the window