Detect usage of aimbot on server side

[PhilippvK]

We should figure out a way to detect the client side aimbot which can be enabled very easy. The is relevant because of #61 as cheating should not contribute to the highscores.

It is up to discuss if players who have the aimbot enabled are allowed to play non-single-player games and if yes, if their aimbot usage should be shown to other players in the UI.

I am aware of the fact, that by the aimbot-checking will be easy to crack (for example by changing the client code) but its better than nothing.