This commit adds the missing feature of allowing the server owner to
provide a reason for kicking/banning a client, which the client sees in
a pop-up window after being kicked. The implementation extends the
network protocol by adding a new network action called
NETWORK_ACTION_KICKED that is capable of having an error string, unlike
the other network error packages. Additionally, the kick function
broadcasts a message to all clients about the kicked client and the
reason for the kick.
5880f1479f