Hide the scrollbar of <body> in RES console

Free up some horizontal space by adding a new class to body which applies `overflow: hidden`, thus removing the scrollbar, then remove the class when RES console is closed.

As far as I'm aware this is the only time RES adds a class called 'RESConsole' to the body tag, there could be a conflict if another RES module adds a class of the same name to body.