Allows sending lines without newlines (to be used with prompts)

By default Evennia adds a newline to every text sent through msg with no way of removing this (at least I couldn't find it...)
This adds a new function on objects:

    def prompt(self, text=None, sessid=0) 

Which sends text to the player without any newline. An IAC + GA is sent instead of the newline, to tell the mud client that it can show/process the line (tintin++ uses this for instance and Mudlet too afaik)