Global info banner for announcements

For announcing system status, very important info about new features, how to use some of the features etc.

Should probably be a dismissible banner or toast of some sort. Ideally the user could dismiss this and then never see it again as long as the announcement doesn't change. Or maybe they need to be able to re-open the announcement once they dismissed it.

For emergencies during peak load times, we should be able to set this message without having to do a pull request with two reviews, a deployment pull request etc.. The message needs to be environment-specific anyways.

The text should be translateable.

While we are at it, we could also make the announcement on the login page dynamic in the same way, to address new users. (Currently "This is the site of the new eCamp. IMPORTANT: This website is under construction. This means that all data is public and will be deleted periodically!")