BUG: Navbar has to change based on is user logged in or not

Currently, the navbar doesn't know whether if a user is logged in or not. The Navbar features logged-in info which should not be visible if a user for example arrives at the page without logging in.

Commit: [b635b1d](https://github.com/JereKoi/React-Diary/commit/b635b1d2866fb447986fe3768ce5092b9d97fdd4)
Date: 28.09.2024