Implement beatmap rating

[48cf]

Explanation of the idea

The funny star thingy at the bottom of results panel. Feels like a nice thing to have 👍

Handling the rating request

Still need to find it out.

Handling the voting

It seems to be handled by the /web/osu-rate.php route, sends 3 relevant parameters: c, u, p and v, respectively: beatmap md5 checksum, username, password md5 checksum and the rating user has submitted.

The v parameter seems to be an integer ranging from 0 to 10, when out of the range, response is "out of range". In case of any error the response changes to "no", or "auth failed" if the user authentication has failed.

Also, when user has already voted on the map, but still manages to send a request, we need to send back "alreadyvoted\n%.2f" formatted with the beatmap rating. If user votes for their first time, the "alreadyvoted\n" is omitted, leaving "%.2f", also formatted with the actual beatmap rating.