Hide admin tabs if not logged in

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Currently, if the website user is not logged in, they can still see all the tabs and even have access to the "Create" page.

In order to add a scoreboard and be able to share the site with players, it would be nice if those tabs were hidden unless the user is an admin of the tournament. The scoreboard from #3 should be the only part of the site publicly accessible.

We also need to think of a way to restrict match creation. For a small tournament, it makes sense that anyone should be able to create one, but not for a LAN. Especially if the interface is going to be available publicly online for players to see their scores.