Allow return status to be specified using quitWithStatus

Call `quitWithStatus(1)`, for example, to exit the program with a 1 status code. This is useful for unit tests and servers. Currently not implemented for Mac platform. Note that I haven't tested the Linux build yet because of VM issues, so I may rebase this at some point so it actually works on Ubuntu dedicated.

EDIT: The reason this is a separate command is because of this:

    GlobalActionMap.bind(keyboard, escape, quit);

This will call `quit(1)` when the escape key is pressed because of the way TorqueScript works (AFAICT). Therefore to prevent incorrect default arguments from being passed, `quit` will always use code `0` and `quitWithStatus` will take an explicit code. `quitWithErrorMessage` has also been extended to optionally take a code.