Avoid errors on first login for new users

When a new user logs in for the first time, they get errors. This is due to the fact that a lot of requests are sent on the initial page load. As the user is not yet created in the database, the backend tries to create a new user for each request that reaches it concurrently, which results in errors. To resolve this, for logged-in users, only the request for the current user state should be sent on initial page load. Every other request (like for publications) is to be blocked until the first user request is finished.

It is important that this change does not affect the website for guest users who are not logged in.