Notification does not update when app is in background

I think we had this problem before and also solved it at some point, but it seems we have a regression.

Steps to reproduce:

• start non-paired mailbox
• put mailbox into background while it is starting up
• on logs, observe that tor gets into published state
• observe that the notification is still "Starting mailbox…"
• switch back to app which should be at the qr code screen now
• observe that notification has now changed to "Waiting for Briar to scan QR code…"

We're collecting the app state in MainActivity only when the activity is started, so it makes sense that currently no updates get processed when the activity is in the background.