Improve Wi-Fi portal notification handling
!1143 (merged) gave us some indication that there is a portal, this MR aims to improve usability:
Keep the portal notification around for up to one minute unless the SSID of the network changes or we get connectivity again. Close it as soon as we get connectivity again or the SSID changes.
I wonder if we should make the timeout even longer like 5m or even persistent (so the notification sticks around until either connectivity is back or the user closes or taps it).
Together with !1605 (merged) the user has a good chance of actually noticing the notification now and we make sure it doesn't get outdated.