0-conf toggle & notifications

[kilrau]

We moved web app to full 0-conf back in June to make sure reverse swaps, especially on mobile, don't fail. Users rightfully recently criticized us for that, we should offer users the option for web app to wait for one confirmation for the lockup tx with a toggle just like we had before. We also want to ask user for notification rights when toggled on and send a notification once lockup tx confirmed to open browser tab and make sure claim succeeds.

Special: on iOS browser push notifications only work for PWAs on home screen: https://developer.apple.com/documentation/usernotifications/sending_web_push_notifications_in_web_apps_and_browsers

How is it for Android? How for Desktop Browsers? Could we even potentially do what Breez does and exploit the minimal compute time one gets from the OS for push notifications to claim the swap?