/whisper command implemented

Usage: /whisper [playername] [message]

I've added a little documentation on *SendChatMessageToAll* because that way people can see what parameters *ClientMessageType.CHANNEL_MESSAGE* requires. Same thing with *SendChatMessageToClient*

Added a new setting that allows you to choose what will be the console's nickname.

Known bugs: replying to the Server PM won't display your message on the GUI.