added the Chat Toggle mod

From mod page:
Do you hate how whenever you play with FTBTeams you have to type ``/ftbteams msg <message>`` just to communicate to your team? No? Well I fixed that anyway! This mod makes this prefix toggleable so you don't have to type it out every time you want to say hi to your teammates! Just type ``/chat toggle`` to toggle between states and ``/chat message <query>`` to change the prefix.