Improve handling of "No institution"

[Kristina Hoeppner]

Currently, "No institution" is the "Site" and has some settings. This is confusing to users as it is listed in the list of institutions, but is not a proper institution, but the actual site. We should improve this to make a cleaner distinction between institutions and the site. Some settings might need to move to "Configure site". I guess, it was implemented on the institutions screen as some elements such as choosing an authentication method is very similar to how it's done in institutions.