Push notification with old login

[tobiasKaminsky]

Push notifications require to have an app password used instead of the "old" login with username/password.
If an user still uses the old login and access the push notification view a fixed snackbar should be shown with "For push notifications please use an app password" (or similar).

(as discussed at conf)

[AndyScherzinger]

👍

[mario]

@AndyScherzinger where's this PR you talk about? :P

[AndyScherzinger]

my mistake, meant "approved"