Add option to mirror the steering wheel

[tomsmalley]

The purpose of this is basically a cheap way of getting right hand drive cars, since many cars are left hand drive. The steering wheel location is by far the most important thing for this: you normally can't see the pedals, and the gauges are not operational in RBR so it doesn't really matter if you can't see them.

This option mirrors the X coordinate of the steering wheel position vector in the SGC file directly. It makes a copy of the SGC file before modifying it, and alters the .ini file to point at the mirrored SGC file.