Emulator UI failed to connect to RTDB over 0.0.0.0 on Windows

Symptoms: https://github.com/firebase/firebase-tools-ui/issues/464#issuecomment-782913719

Environment: Windows (with Chrome and maybe other browsers), when RTDB emulator is set to listen on `"host": "0.0.0.0"` in `firebase.json`.

Root cause: firebase/firebase-tools#2870
Workaround: https://github.com/firebase/firebase-tools/issues/2870#issuecomment-738189582
tl;dr: Run `localStorage.removeItem('firebase:previous_websocket_failure')` in Developer Console on Firebase Emulator UI web page (NOT hosting emulator or anywhere in your app)

We should either bake the workaround into Emulator UI or fix the underlying issue in RTDB (cleaner but may take longer). The workaround above can be used to get it working for now.