Automatically set the users' affiliations on login

Currently, the users get their user profile initialized with their full name, but not their affiliations. Right now, this is always "TU Wien" by definition. So for the time being (until we enable authentication for externals) we could hard-code this value whenever the user profile is updated from the information given by the authentication system.

This is what it looks like right now:

This is what it should look like:

---

Note: Setting a user's profile doesn't seem to work like this:

user.user_profile["affiliations"] = "TU Wien"

Instead, it looks like we need to do something like:

user.user_profile = {**user.user_profile, "affiliations": "TU Wien"}