Limit possibility of brute force attacks when guessing password

As suggested by elexis, rP24728 should get some protection against brute force attacks on password.

This is supposed to prevent attackers from getting connection data by guessing the password.

Each failed attempt increases the counter.
XmppClient on the server side checks for the users with certain number of failed attempts, determined in CNetServer, and refuses to check the password, answering with banned message.
So they cant guess again in given match. Effect of this block will dissapear after new match is created.

Differential revision: D3467
Comments by: wraitii, Stan
Tested by: Stan, Freagarach
Ref: #5913