Added a Block Function

Cheaters in any game are annoying. In Pidro a cheater is considered a person who is about to loose a game, leave it before the score is calculated.
I have this idea to assign scores to a player after the fact, so that you get the loosing score no matter when you leave the game, but that's a bit more complicated. So we came up with a block function that is easier to implement. When you block another player, this person will never show up in your realm again, meaning you won't see her in your lobby or anywhere else ever again. That way you can sort out the sour apples yourself for now :)