Admins should be able to ban users

[josecelano]

Parent issue: #657

We need to define what restrictions a banned user has. What would be the difference between banned users and disabled users?

I think it could be temporary, and while the users are banned:

• They cannot upload torrents
• Their tracker kyes are revoked

NOTE: Although the Index (API) implemented the ban logic with a banned users list, it currently has no effect, and it's not possible to ban a user from the UI (admin panel).

WARNING: With the current Index behaviour, the admin can ban themselves. If they do, they will not be able to unban themselves. The only way to unban themselves is to manually remove the user from the banned user list in the database.