mark alerts as alerts
mark alerts as alerts

I think that these messages should be announced on page load. I hope
that this change has the desired effect. In orca at least it did not
change anything.

Bootstrap does the same:
https://getbootstrap.com/docs/4.0/components/alerts/

liqd/a4-meinberlin,liqd/a4-meinberlin,liqd/a4-meinberlin,liqd/a4-meinberlin