Adding global chat keybind

We discussed adding the features of my Lightning keybind mod into the Undercast client last year, but I never got around to it. I decided to try it now.

Basically, I added a keybind ('Y') that opens the chat gui and pre-loads it with "/g ", thus making it easier to global chat. I also shortened one of your keybind conditionals (compressed two if statements into one with the && operator).

The other feature I would like to add in the future is a team selection gui, where you press a key and it pops up the list of teams, but that is for the future.