Design status UI for mailbox connection
would be nice to have a place in the briar app to show the current status of the mailbox connection (like we do for tor).
in case there's a permanent issue with the mailbox, we need to surface this in the UI and alert the user, so if the mailbox is lost, the user can fix it or let us tell all contacts to stop using it.
it might be interesting to know which contact supports/has a mailbox