Castaway/704 check for updates immediately

[castaway]

Fixes #704 .. or improves anyway

[castaway]

Not entirely sure this works yet - isStable apparently only gets stable if no polling things are started/happening, so may need to check those too.

This can be improved by using activateUpdate instead of window.reload, and then subscribing to "unrecoverable state" to reload in case of issues, see https://v11.angular.io/guide/service-worker-communications